So I sent my UK editor a link to this poll and also expounded a little on why I thought that "Timothy" was the best name for the character, and she (being a lovely and understanding person) said that was just fine. This was a great relief to me, especially since my dutiful attempt to substitute "Tim" for "Timothy" throughout the narrative yielded a truly soul-harrowing result (I couldn't get past the first page!). And besides, I've known this character as Timothy since he first appeared in the original draft of Knife back in 1994, so it would have been very hard for me to change it (even if I did cut him from the final draft).
Anyway, Timothy he is and Timothy he shall remain. Huzzah!