If you don't get a satisfactory response here, consider posting the question to the perldl mailing list. There's at least one active list member there that uses TriD fairly heavily and may be able to help. Of course, there may be the same (or even better) assistance available right here.
There's been quite a lot of PDL material recently so
I think once I go to sleep the night-shift
Perl Elves
will wake up and prod me in the right direction.
I didn't find anything in the PDL archives or code though...