How would I make an item share the index of another?

If you're confused as to what I mean, I would like to make a sinew item that is dropped by pigs and shares the same index as string. This would make it so whatever recipes string is included in, sinew could be used as an alternative, similar to how wood works in some recipes. I first thought to make the same recipes as string with sinew, but that wouldn't make the two interchangeable nor would allow it to be used with other mods in a similar fashion. Any ideas or ways to do this?