http://bike.shimano.com/publish/cont...structions.pdf
The actual internal installation is a bit of a pain, I thought I read somewhere you need to get certified by Shimano to mess with it but that might be from the mechanic end of things. I recently did an internal light to bottle cage mounted battery pack in the top tube for a customer and he asked about doing this also and in the next sentence asked about installing travel couplings, so I passed on the whole enchilada because of the lol factor.
Your problem is any builder doing ti is going to butt up against your budget before even considering the internal wiring issue.
Why not drop Ti Cycles a line in Portland, Oregon and ask, I believe they have the expertise in this.