I'm sure there are those out there who are acquainted with ParaGrafix, well they have a tool for folding photoetch that I think would also be handy for folding those small paper parts more accurately. I'm ordering one for folding some photoetch but I'm going to be trying it for paper also, check it out at this link.
http://www.paragrafix.biz/product_detail.asp?MainCat=Tools&SubCat=blank&PPartNum=PFT-5
http://www.paragrafix.biz/product_detail.asp?MainCat=Tools&SubCat=blank&PPartNum=PFT-5