You leave the welded in caps in on two sides and I'm betting you can cut the grooves with a side cutting Dremel bit and use a dowel as a spacer you can get ± two thou tolerance. See if you can find YouTube video. The main problem is it'll be impossible to get the size until you pull out the old one.

__________________
2011 E70 • N55 (me)
2012 E70 • N63 (wife)