Bike Fitting/power Question

Is there a way to measure power (without a Powertap) when dialing in your bike during a fitting?  Can a Computrainer accomplish this?

I am looking to get my bike re-fit after my seat post sank ~ 1 cm over the season ... and I believe that my fit may have changed over the course of the 2200+ miles I have put on it since last April when I purchased the bike (hopefully I am more fit and limber ).

Looking to see the best route to get the fitting done.

Suggestions?