Cute. Cute. He did help, it's true!
The first most obvious thing for an anti-sword to do is healing. But of course healing is a lot harder than destruction; there are a lot of ways you can change something that will break it, fewer that will repair it. So he'd have to think very carefully about how to waste most of the power of all that spellfray on things that don't matter and can't get big enough to do any damage, and only let through the tiny fraction of it that actually wants to do something helpful. (That's an oversimplification. It's not that specific bits of spellfray 'want' different things; it's all sort of sloshing around wildly doing this or that, and if you're careful and clever and a little bit of a reckless idiot you can figure out how to bend it away from what it's in the middle of being about to do and push it into something else instead, but you can't get too far from its original purpose and you have to do it much too fast to be able to save any of it in the moment when you have a spell going wrong; his sword used layer after layer of redirection, to catch it all and funnel it into the destructive effect he wanted, but because 'destruction' is so much broader a target it only took a few layers, doing the same for healing would be much more complex and delicate work...) Anyway, the main trouble with healing is that you can only do it when someone or something needs to be healed, which won't be all the time, so his anti-sword might spend a while being overcharged and that's not a good way for things to be.
Then there's water, which is springing (so to speak) to mind because they're walking in a desert. Making water is probably easier than making healing, because there's a sense in which the target is broader—it's hard to explain why; it has to do with things he feels more than knows, his practiced sense of which ways magic is more and less eager to turn—but he's not sure how useful it will be. Well, obviously water is generally useful in a desert. But he's not sure how much water he'll get at a time, and he sort of feels like even in a desert, dumping out several wagonloads at once in an inhabited area is maybe kind of still a destructive act.
Then there's the concept of a shield, one that could potentially redirect these 'bullets' Zash mentioned to make them miss anyone in range. That would be tricky for a number of reasons, not least the fact that it would screw with Zash's trick shots unless Siran put a lot of work into figuring out how not to. But it's a pleasing image, and he thinks motion might be a fairly broad target as these things go, maybe broader than water. It has the same problem as healing, though, in that you can only use a shield when there's something to shield against.
He could, he supposes, also try combining all of these effects into a single item. He's not sure what shape such an item should be. A... shield-wand-cup?? Well, the shape doesn't really matter to the magic, except to the extent that it makes Siran's work easier by making him feel like it's more naturally inclined to the purpose he intends. Anyway it would be a beastly amount of work to set all that up and have all the different parts work without interfering with each other, but if he got it all set up just right, it'd help make up for the comparative narrowness of all these targets. He suspects, though, that if he did it this way it'd be harder to avoid the big obvious problem of any spellfray-absorbing artifact: the fact that inevitably a little bit will leak out around the edges. With the sword that wasn't so bad, because the sword's job was to obliterate things and it didn't matter much if in the brief final moments of their existence it also turned them purple or made them burst into song. Rather less convenient to have random magic effects on the several wagonloads of water you just dumped in the middle of the street. (He's imagining a rainbow flood singing thirty songs at once and it's quite the mental image.) And he thinks, the less unified in purpose his artifact is, the more it will tend to do random things and the bigger those random things will tend to be, unless he puts a whole lot more work in to mitigate that.