I have a TCR-1. The TCR series is a really good road bike and can be set up as a decent bike for tris. Let's not forget that Luc VanLierde won IM Hawaii with the fastest bike split on a TCR in 1999. There are two ways to set up a TCR for tris that I've tried.
1) Forget about going to 78 degrees on a TCR. I tried it with with a Profile forward seat post. It throws the bike off balance with too much weight forward since the TCR is designed as a road bike. However, it works very well at 75-76 degrees, which is what the Team Once TCR TT bikes run with their custom frames. This can likely be accomplished by jamming the seat right back on a forward post or a better alternative would be to spend forty bucks on a M2 Racer seat shifter. This is new on the market and should allow you to dial in your seat position accurately. Just got one for X-mas and it looks as if it works really great. You'll be moving your seat three or four cm forward so also drop your bars as to have the same effect as lengthening your top tube. This will also allow you to get more aero. I could get quite low on my TCR with the 75/76 angle. I"ve used Syntace C2 aero bars with this set up and they work great. Here is a nifty site written by Dan Emfield that has a chart that shows how to figure your approximate seat tube angle by measuring the saddle tip with a plumb line in relation to the BB and saddle height.
http://www.slowtwitch.com/...techctr/bikefit.html 2) The other alternative is the "big slam" position as described by John Cobb. Jam your saddle right back, lower your seat by about an inch and get a pair of the big slam specific Profile Jammer GT aero bars that are shorter than normal tri aeo bars. You may also wish to run a slightly shorter stem than normal. You are now mimicking a riding position like Greg Lemond, Steve Bauer or a number of the current Euro pros at a seat angle of 72 degrees or so. According to Cobb and some others, this is a more powerful position to ride in, at least for some people. There are three articles available in the "tech section" regarding the big slam and another article in "Dave's Page" Check it out.
http://www.bicyclesports.com/index.html