Not shown: I do have a tiny table saw meant for cutting molding and little stuff that was used to cut the frames of the tweeters. It can't angle, though, and is too small to cut as deeply as would be needed anyways.
Tweeters were glued together between two scraps of wood to keep them straight, then one end was screwed to the array upright. The other end was screwed to a board, and a section of 1/4 ply was laid alongside it to support the shoe of the circular saw. A guide board was added to run the circular saw along, and then it was a surprisingly easy cut using the standard general-purpose blade.
Multicolored hair ties were then used to hold them together over a corner jig.
I'd still feel WAY more comfortable doing this on a table saw, but it can be done!