Does this do what you want?

my $a = chr(65);
my $b = chr(66);
my $c = chr(67);
printf "%s" x 3, $a x 2, $b x 3, $c x 4;
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Update: or perhaps this?

printf "%c" x 9, (65) x 2, (66) x 3, (67) x 4;
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or even, using james2vegas' "$" idea, but with %c instead of %s

printf '%1$c'x2 . '%2$c'x3 . '%3$c'x4, 65, 66, 67;
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BTW, the above strange-looking POSIX extension positional parameter $ printf syntax was introduced in Perl 5.8 in 2002.