Great description mherdeg ^ and if I may add, where you say "convince any gate agent", I'd like to add that if it is an airport that has a dedicated customer service location (i.e. SFO near gate 80-82 or IAD which has 2 [or 3?]), you can also try there as the folks that work the customer service counters are generally gate agents as well and can do the same thing (the customer service folks at SFO were able to do just what you described for me in less than 3 minutes)