Simply re-posting essentially the same question you posted three days ago (Signal Handler) is unlikely to provide any new insights — in particular as there don't seem to be many alternatives...

As I already said in that thread, use Perl 5.10.0 and extract the respective PID from the raw siginfo dump using unpack. Have you tried that (i.e. with 5.10.0)?  The only alternative I see is writing your own XS code... but then you'd have to make sure it doesn't interfere with Perl's already existing signal handling implementation, which could be non-trivial.