Wow! 3x12mm thats a serious tab, really doubt it would go on these parts IMHO.

One idea I just had was to split the job into two overlapping parts and use solid clamps with a pause in the job to allow two new clamps to be set over the cut part and the other clamps to be removed. It would mean double the tooling changes but might work?

There are no holes for fixings internally.

I was using 1300mm/min and 2.5DOC for the 5mm single-flute tool.