"DOLLARUA" and the various other promotion profiles almost always have a big list of things with which they are not combineable -- generally other discount coupons, status (e.g., youth or government) fares, and so on. Right before that laundry list in EVERY UA promotional profile I've ever seen is "EXCEPTION: MAY BE COMBINED WITH TRAVEL CREDIT/TRAVEL VOUCHER." For the Entertainment coupon, point the agent to the ENT03 profile (or whatever it is this year), and if they read hard enough they'll find that exception. As always, it's right above the list of things it CAN'T be combined with.

This is one of those situations where the agents often become very defensive and refuse to do the research. However, as you're 100% right, being patient and polite will tend to get you there sooner. By the way, travel agencies *can* do this too if you have a good relationship with one. If you don't, this type of transaction tends to attract a fee.