Get a sheet of 1/16 to 1/8" or similar rubber from either your local rubber
parts store or part of an old inner tube should fit round your wine bottle
and cut out the letters you want. Use a knife or scalpel blade and do it by
hand. A bit of soapy water will help, and bending the rubber to open the cut
a little will allow you to cut easier. Use colour pencils to draw your
pattern on the rubber before cutting and you may find it easier to cut a
shallow track then bend and stretch it while going deeper.

The rubber can be sticky taped to the bottle to hold it in one place, and
used with a thin layer of rubber glue or silicone sealant for the fiddly
bits, but experiment with a couple of bottles first, which of course gives
both of you a good reason to consume them.......

The rubber stencil should last long enough to do all 40 bottles you want to
do, as long as you are gentle with it and don't blast too close or hard on
the fine detail.

Another that I haven't tried, but might also be good is the flexible plastic
(Teflon?) kitchen cutting boards from the dollar shops. There are also
simple plastic stencils at a number of craft shops, but these may not go the
distance with the sandblaster.

Hope this helps.
Peter