How do I transfer to a full world in Guild Wars 2?

It's unclear whether the population of a world is based on the number of players currently online or the number of accounts on that world, but population levels do fluctuate over time. As such, it is possible to transfer onto a full server by trying at a different time of day.

Try checking during off-peak hours, such as early in the morning. I've heard from several guildmates that they've had success transferring onto a normally "Full" world this way.

No there isn't - once a server is full, it means you'll need to wait until somebody transfers off that server before you will be able to move to it. While a server is marked as 'full', this means it is locked for transfers to it, or initially associating your account with that server (setting your home server).

Here is an official source from 'CC Eva', a community coordinator, explaining how server capacities work:

when you see a server FULL means that the people who’ve chosen that server as theirs, or players who have moved to that particular server, have reached the cap, independently of where did they create their accounts.

This means that the number of accounts with the server as their home server has reached the capacity cap set for that server. Over time if people move away from the server it will become available again for new accounts to choose as their home server.