Unlock cleat from clipless pedal

I had a (improperly tightened) bolt drop out of a SPD cleat while riding which left me in the same predicament (also ended up eating asphalt), I ended up being able to wedge my shoe against the frame to get the appropriate leverage to kick the shoe/cleat combo out of the pedal.

I would try attaching the pedal to a bike (and foot in shoe) and attempting the same move. You can always unscrew the pedal and take off the shoe to get back to where you are today.

EDIT: I misunderstood your situation hence my original answer. In the case that your shoe is still stuck to the cleat, remove the pedal from the bike first. Keeping the pedal on the bike will just restrict your motion as the crank arm and frame will get the in way.

Put the pedal in a vice grip or between two solid objects which allow you to keep the pedal still. Then simply twist the shoe in the normal unlocking direction until it disengages from the pedal. Having the pedal off the bike will allow you to turn the shoe a whole lot further and allow you to unclip. I don't suspect you would cause any damage this way.

Removal if it's just the cleat stuck (not on shoe)

Firstly make sure that the spring tension on the pedal is all the way down. This is lowered by turning the little hex / Allen screw to the left as much as it will go. Releasing this tension on the spring will make the job a whole lot easier.

Then use a set of needle-nose pliers to twist the cleat, simulating the twisting of your foot as you would when it's attached to a shoe.

If this doesn't work, you can try and use screwdrivers to pry the tensioned 'catch' away from the cleat, hopefully releasing enough pressure to twist it and remove it.

In terms of damaged caused, you may scratch the cleat and/or pedal, but I guess no more than you would by clipping in and out and walking around.

Assuming that the shoe is still attached to the cleat....

Can you not just keep turning the shoe to a wider and wider angle until it forces the cleat to disengage from the pedal? You'll scratch the sole of the shoe, and possibly slightly widen the screw holes in the shoe, but it shouldn't break anything.

Note that it's quite hard to get a shoe & cleat out of SPD pedals using your hands - even when the cleat is screwed on correctly. It's much easier to do when you are wearing the shoe. I'd recommend trying this whilst wearing the shoe, sitting on the bike, but leaning against a wall or fence (or having someone hold you upright).

You can use a pipe wrench -- the tool you use for plumbing pipes -- to clamp the cleat and turn it. Just be careful not to break anything.

I removed the insole of the shoe, placed the Allen wrench in the hole left by the loosened bolt. I then aligned it with the hole the bolt goes in to the cleat AND THEN turned the shoe and it popped off...

I had the same problem but it "turned out" (pun?) that I needed to just twist the foot like it was on a turntable with the force of opening a jar. I was trying, mistakenly to tip it out and to the side, like a boat tipping over. The latter doesn't work.