Since you gave EYKIW all of 10 seconds to answer your question before running back to PLEBA, I shouldn't help you with this.
However, if you want my advice... do NOT sell those tickets - at least not yet.
Once everyone starts getting their tickets, including those from Propaganda, you'll see tons of people wanting to trade or sell. You might have to do some serious "wheelin'-and-a-dealin'" but having tickets in your hand gives you some bargaining power right away.
Since GA tickets are primo for this tour, you might wind up trading your tickets AND still having to pay a little extra for the swap. So set yourself a limit on what you are willing to do (swap, buy, etc.) and what you are willing to spend (nothing, $25, $100) to get GA's.
Then, check ALL the popular forums on Interference. Check eBay. Check Yahoo auctions. Check WIRE. Check other on-line U2 groups. Eventually, you might find what you seek.
If you don't have that type of time, you could see if TicketMaster or the box office at the venue has tickets available the day of the show. But be prepared to spend time in line. And keep in mind - the time you spend in line hoping to get GA's is time you are NOT spending in line to get a good spot in or around the heart! Plus, there's no guarantee that the Box Office or TicketMaster will have extra tickets.
In other words, do NOT sell your tickets until you have found yourself a pair of GA's. Only then sell your tickets (unless, of course, getting GA's meant a swap of your tickets). If you sell your tickets now, you might not get any GA's - then you can't go to the show at all!
If you do buy/trade for tickets, I HIGHLY recommend using PayPal and FedEx WITH insurance to protect your transaction. PLEASE be careful of the thieves out there.
As for "sneaking in" the heart - I wouldn't count on it. While DB9 (DiamondBruno) managed to leap on the stage, the overall security at the shows was rather tight. One needs writsbands and ticket stubs to get in the heart. There was a lot of security at the Boston show when I was in the heart. And now, due to the tragedies of Sept. 11th, I imagine that security will be at least double (especially at all U.S. events). Therefore, I doubt you'll be able to "jump barriers" to get in - most likely, if you try you'll be booted out of the venue. Just get your GA's and you'll be fine.
Good luck!