Please check out this reddit discussion: https://www.reddit.com/r/Monero/comments/44abpz/question_how_can_i_create_an_unsigned_transaction/

According to fluffyponyza, a bulk of the work has already been done by moneromooo.

Now it's a matter of figuring out a good format for those unsigned and signed transaction files.

Anyone care to look into this?

And if it needs funding, how much are we talking about?