Maybe a quick solution is to create tmcommand, input: none, output:discard
with the command:
open "txmt://open/url?line=$TM_LINE_NUMBER&column=$( perl -e ' $a = $ENV{"TM_CURRENT_LINE"}; $a =~ s/^\s*//; $diff = length($ENV{"TM_CURRENT_LINE"}) - length($a); print ++$diff; ')"
Cheers, --Hans