Hmm, while regular electrical tape is only rated for 600V, Scotch-brand
"splice tape" is rated for close to 22kV. Of course that's *through the
tape* though, so although it would insulate the conductors from the outside
world, it's not clear how effective it would be at insulating the two
conductors that are only a couple of mm apart; the tape doesn't really play
a part in that scenario, only the glue.
Given that flashovers don't seem to do any damage, I would be inclinded to just
try the tape first and see if it will stand up to the voltage. If it is only 3kV, I
suspect
it will. I would not start cutting the flexiprint unless you have to.
-tony