There are 4 options:
1) Slot with file (most common option)
2) Fill mounting holes with molten steel and re-drill.
3) Drill out mount hole to larger size and get some offset bushes made up
4) Change position of mounting bolts on strut.
1,2 and 4 have all been done before to my knowledge. You *might* get an Engineer to approve 2,3 or 4.