"Virtually" Splitting Albums

[stefano_mbp]

You could try to use DISCSUBTITLE tag as described here
This is mostly used for box sets but works fine in your example too, you need to renumber discs and tracks according to DISCSUBTITLE tag where each DISCSUBTITLE must be assigner to each “disc”.
In your example it should be:
1.1 Bonus tracks
2.1-2.x Soundtrack
3.1-3.8 Bonus tracks