At the moment you can't, in UK the keyboard product code now ends MC184B/B, these do not have the function keys working, the older MC184B/A keyboards do! I am in the same situation, if you look at your keyboard I bet the F4 key has 6 squares on it? This is a lion shortcut, older keyboard has different symbol.
I have asked apple who told me that it wasn't a known issue, and so when 5 is released it may or may not fix the problem..
Their suggestion, find an older keyboard, but if you look many people are having the same problem, not just with the iPad 2, so hopefully IOS 5 WILL sort it out, I can't find a new older product string keyboard to buy, shame love the keyboard, just wished it worked fully.
Hope you find an answer, if I hear of one will post it.
Thank you Boromirinda.
you were correct. here the model number was MC184LL/B, which is the newer keyboard designed for lion. i went out to a radioshack and found an older MC184LL/A keyboard, which actually if you look at the above wiki liink, are both the latest model (a1314). the (A) model works perfectly with the ipad and iphone, all the special function key work as they should.
so for those that are expirencing that same problem. if your keyboard has the 6 small square on the F4 key and the there is not a border around the 3 small sqares on the F3 key it is indeed a (B) keyboard made for lion and limited compatibility for iOS devices.
the (A) keyboard will have a dashboard dial symbol for the F4 key and a box outline around 3 smaller square on the F3 key. this keyboard will have full compatibility with all iOS devices to be able to control the brightness, mute, volume up and down, and also play/pause skip and reverse.
i have gone through 2 different (B) keyboards thinking it was a glich and now an (A) keyboard which works perfectly.
Just thought I would post this here, finally managed to get my hands on the older A1314 : MC184B/A is the model number here in the uk, and guess what?
Despite being told by the Genius who called me up, saying that the function keys not working was nothing to do with the model of keyboard I was using and that either my Ipad was at fault, the keyboard or me..
It WORKS FINE..
Kudos to Apple for following it up, but listen to your community, we worked out the problem while you still haven't noticed one....
Anyway all is well with the world, I can type and control the music while I do it, all from the comfort of my chair while the Ipad stays docked out the way..
If only everything could be fixed so easily
To all with a MC184B/B keyboard where the function keys don't work, swap it for the older MC184B/A, it works 100% and saved me £15, Apple online £57.00, Viking Direct £42.00 from the clearance section