I'm surprised no one has asked yet about the level of accuracy you require. If you're talking fractions of a degree then certainly a sine bar/plate setup is the most likely candidate.
However, if you can live with it being off by maybe a degree of two you can probably set things up using a plate protractor and/or a magnetic dial protractor (Google it). A universal bevel protractor will get you even closer. Carefully shim things up to the angles required, making sure that it's well-secured at the same time. Light cuts and lots of clamps. Aluminum cuts like wood if you're careful. You may be able to get away with using wood as shims or cut the compound angle out of wood on another tool (compound mitre saw, table saw) and use it as a mounting base. Hell, you could even cut something from aluminum on one of those.
Depending on your lathe, you may be able to secure the works to the cross slide. If it's a through hole, consider line boring. If not, it may still work with an adjustable boring head in your 3/4 jaw chuck. Did I miss the size of the hole? Maybe you can just drill it? I like this thought much better than the whole mess spinning on a face plate.
Again, make sure it's secure and don't go blaming me if you get it in the teeth... :P