Now you've gone and done it, you've made me actually start paying attention to this thread again!
The point I'm trying to make is that GregTech will most likely function on the first item in your inventory that an inventory scanning function written into code for the soldering iron comes across and will just not care about wasting an entire ingot over a fine piece of wire. If you don't get that, go back under whatever it was you were under previously. It's not safe out here.
Jason probably could configure it not to accept certain forms of items, if he really wanted to. But that would take a bit of research and effort on the part of him and others who tinker with the minetweaker scripts and related item usage functions they're using from GregTech. It's therefore probably quite difficult for them to understand why you have a frustration with the wrong item being used when it might be something Greg himself programmed for whatever reason.
So, if you really want your soldering iron to only use certain items then you probably should consider looking into the associated functions in the code and making a submission to them to have parts of it changed. Jason would certainly appreciate your contribution, and you'd learn just how complicated it is to debug something like wrong or incorrect item usage. ;-)
Have a nice day ... night ... whatever!
Cheers ...
BrickVoid