Yes there are feedback controllers but all the one's I've seen are in the $2,000 to $4,000 category but if you don't mind the bucks it's available. Here's a couple I found:

http://www.amerimerc.com/pool_supply...rs/CAT4000.asp
http://westernpump.ca/pages/spa/controllers.htm

We didn't want to worry about all the start-up swings affect on our heater so we simply added a bypass valve to isolate it from the system when not in use.
Jo