I was just thinking about Tim/Jim the other day. This is why it doesn't work,
Timothy isn't "long" for
Tim,
Tim is short for
Timothy. So even thought
Jim and
Tim sound alike, it doesn't mean that they should both be short for similar names. That's like saying "well,
Abby and
Addie sound a lot a like... I think I'll name my kid Adigail.".
I realize that you're not considering naming a human this but it's just not nice.
How about
Timothy Grey or
James Greg?