Hey there, welcome to this great Wii community, great to have you on board.
You have quite a predicament. You could purchase FreeLoader (Pal Version) but as you said about the 3.3 forced update, which in itself is dangerous as it will brick your wii since the game is NTSC-U and free loader not working with 3.3 anyway so this goes out the window. So here is what I believe you will need to do:
0) Do not update your wii to 3.3E ...yet
1) Install Homebrew channel using this guide ->
[Only Registered Users Can See Links. Click Here To Register]
2) Get GeckOS from here ->
[Only Registered Users Can See Links. Click Here To Register] you may also want to readup on how its used in their forums/faq
3) Update Wii to 3.3E from your Wii System menu (Not from game)
4) Use load GeckoOS within Homebrew channel and load your Rockband game
5) Accept hugs and kisses from kids