Console commands work in the demo.
Spoiler!
go to the demo folder (For me it's c:\program files\dragon age 2 demo\). Open up the bin_ship folder. Find DragonAge2Demo.exe, create a shortcut for it on the desktop. Right click on the shortcut, select properties, and then where it says Target add the line " -enabledeveloperconsole" (with the space before the dash, but without the quotes...).
Start the demo from the shortcut...
Once you're in the game, the tilde key opens up the console. You can't see what you're typing, but it does work, I've leveled my characters up to 15 (it takes about a million xp to level to 49, apparently the highest you can go).
The command for adding xp: runscript addxp x (x being whatever amount you want to use...)
I'd never use the console in the real game, but it's fun to play around with in the demo to see some of the skills you can't normally get to...
Thread on the bioware forum with more info:
http://social.bioware.com/forum/1/to.../index/6169685
And it's just me being paranoid, but I made sure I wasn't logged into EA when I ran the console. For whatever reason.