As said, it won't fit without radical & irreversible physical intervention. The inability to use EF-S lenses on the 10D makes it a bad choice for an only camera..
Being used to a 10D, for a cheap upgrade he should definitely think about is a 30D or newer xxD body (or steal your 7D) as the more consumer-oriented xxxD models have a bit different (and much more menu-driven) operation logic. He'll be very frustrated with it.