Just cancel the IAH-SFO segment. That will create a credit for the value of the segment. You would then pay a $200 penalty in new money in order to use that credit. But, if you don't use the credit, you won't ever pay the penalty. Same thing as a no show.

Alternatively, have you priced changing your ticket from IAH-SFO to IAH-SFO-BDL. You may be surprised at the pricing. The other approach is to simply fly IAH-SFO on a carrier other than UA. While that means a connection, at least AA has significant frequencies via DFW. If you do go the "no show" route, make sure that you check whether the flight is substantially delayed or cancelled. You may then request a full refund of that segment.

Finally, do not try to scam the system as suggested elsewhere in this thread. UA's systems are much more sophisticated than suggested. Dropping your middle initial and the like won't do anything for you other than flag you to the system even quicker.