Is a high alpha sideslip possible and safe?
You would be risking your life.  Cross controlled approaches should only be done well above stall speed and only after testing at a higher altitude.  Increasing AOA will slow your plane down.  If you recognize being high early in the pattern, you might be better off going ABOVE Vbg and slip, which makes the plane glide much less efficiently.  Spoilers act in a similar manner.

Do a proper approach and use your flaps/spoilers.  If it is allowed, forward slip to increase rate of descent at your preferred approach speed.  If you can't make the runway GO AROUND.  Changing speeds on short final will make judging the landing much more difficult.

In an emergency landing it is far better to over shoot the field and roll into fence, trees, etc at 10-20 mph than to risk losing control of the plane.

As a side note, only deltas come close to 30 degrees AOA before stalling, and these tend to drop like a rock when slipped if their vortex lift is sufficiently disturbed.  Slats and flaps will significantly increase stall AOA, but at the expense of much more drag.

Generally a bad idea.