It's not clear to me what your problem is. There's no problem in running concurrent repeat execution "threads":

use Tk;
$mw=tkinit;
for my $i (1..10) {
    $mw->repeat(rand(900)+100, sub { warn "I'm $i.\n" });
}
MainLoop;
[download]

(At least this works on Linux).

However the repeat callback blocks while it is executed. If you want real threads, then you have to use real threads, or fork a process. But note that you must not call any Tk-related functions while executing the thread --- Perl/Tk is not yet thread-safe.