I did it even if the names on the battle.net accounts didn't match. I've talked to a GM and put him verify the IP addresses I was logging on both accounts to verify my identity.
While I'm not surprised you found a gm that would agree to that, I can see it not working for every time. Changing the names to match would probably increase your chance if trying to ticket for it.
Actually if you log into your Battle.net account, click on Account at the top and then be in the Summary section, there's a link on the right hand side that says "Merge a World of Warcraft Account".
As it has already been mentioned this doesn't work if the trial account has its own battle account. It will only work to merge older world of warcraft accounts that are not already part of a battle account.
Ticketing a GM has worked for many people and I'm sure it would for you as well. The other option is just to call blizzard support, took about 15 minutes on hold followed by a 2 minute conversation with a representative in which all that was required was to read off the code from one of the wow disks, the upgrade code sent to you if done online, to prove that the full account was mine. Login and password was enough verification for the trial account.
One thing to note, while mounts will be shared across both accounts, and any new ones created under the battle account. Battle pets available come from the main full account so any battle pets picked up on your trial will no longer be available even on the toon which originally received it. This can be ticketed, or cleared up in the same phone call that merges the accounts. As for tittles and tabards, I was told that like mounts they should be shared both ways after the accounts are linked, unfortunately as I did not have any on my trial that the account I was linking to didn't already have I cannot verify that this works correctly, though I would assume this can be cleared up with a ticket or call like the battle pets.
Good luck merging them, I hope it works out well