If it's not too deep, and it's a lathe job, you could swing the compound to 46 degrees and use a conventional single-point boring tool
If you have to do it with a re-ground drill, first use conventional drills to take as much meat out as you can. Then take a piece of tough rag (denim's quite good) say 2.5" square, fold it enough times that when you lay it across the hole like an elephant trap it will overlap the rim, but not so much it prevents the drill from stuffing it right on in there.
Wet the rag (before folding) fairly liberally with top grade neat sulphurated cutting oil, and just plunge through it, using really heavy feed.
The rag compresses up and provides industrial strength vibration damping, plus the extra feed force preloads the bearings, quill feed etc, so the beneficial effect on chatter is quite surprising. The chips embed into the rag, if there's lots to come out you'll have to replace the rag a couple of times.