David Merrill wrote:

Just had the house re-plumbed with PEX because of acidic water erosion. The
plumbers cut off and left the old copper pipe stubs protruding about an inch
from the drywall behind toilets and sinks. A much larger hole would have to
be made in the drywall in order to amputate these with a mini tube cutter
behind the drywall prior to patching the drywall. Internal pipe cutters
that I've seen are too large for 1/2 inch copper. Google search didn't turn
up anything readily.

Is there a better way ? Surely I'm not the first to encounter this problem.

You've got a couple holes to patch, anyway...I'd just cut a even section
out, cut the pipe off and then replace the patch. If you don't get the
pipes out of the hole it would be hard to keep the patch from cracking
around them anyway.