Not an answer to your question, but

(my ($d1, $d2, $d3, $d4, $d5, $d6) = $_) = m/$regex/;
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would more naturally be written as

my ($d1, $d2, $d3, $d4, $d5, $d6) = /$regex/;
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which is the same as

my ($d1, $d2, $d3, $d4, $d5, $d6) = $_ =~ /$regex/;
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(The temporary assignment of $_ to $d1 in your variant doesn't do any harm, but doesn't help much either.)

Update: as for what you're attempting to do, IMHO, it would be a perfectly sensible thing to want to have as an option  (I also would have had uses for it occasionally).

However, AFAIK, there is no way to do it, except if you implement it yourself with (?{...}) code or some such (as shown further down) — which of course ruins any elegance the approach might have had otherwise.