I've written a module to solve your problem directly; it uses tied strings. See Tie::Scalar::Substring.

In your case, you could use it like this:

$sequence = 1234567890;

my( $frame1, $frame2, $frame3 );

tie $frame1, 'Tie::Scalar::Substring', \$sequence, 0;
tie $frame2, 'Tie::Scalar::Substring', \$sequence, 1;
tie $frame3, 'Tie::Scalar::Substring', \$sequence, 2;
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