Unbolt the whole steering column with the mechanical part of the lock. You will need to cut grooves in the 'head-snap-bolts' to turn them after you release them with a small chisel. Easier than it reads, I've done it. Bollts can be replaced with Allen cap head type. Once it is out you can engineer the release of the unit and repair as required.
Good - Fast - Cheap: Pick any two.
E23 735i; E32 735iL (X 2 - 1 Alpine White and 1 Glacier Blue); E34 535i; E38 735iL; R50 Cooper; R55 Cooper Clubman.
E21 318i; E30 318i; E32 735iL; E34 535i; E38 730iL; E53 4.4i