If you want to ride 100 miles, just do your own ride.
I abhor the thought of asking people for money. The only charity rides I've done are ones where you just pay a registration fee. Seriously, I wanted to do the Soldier Ride a second time, but they added in fund raising commitments. Sorry, I just can't do it. I won't ask work colleagues and I can't ask friends.
And I've heard that some of the TIT coaches around here are not so nice...