If you want to customize the completion on a per-script basis, then one way to approach this problem would be to use bash_completion with a custom completion function. This function could parse the given perl script for completion hints which could be passed to compgen (a bash builtin).

I haven't worked with bash_completion enough to provide a working example unfortunately. One potential shortcoming would be that you need to tell bash when to run this completion code. This is typically done by specifying the completion logic for a given command. (e.g. perl is handled by the _perl function).

Example code with completion config in comments

#!/usr/bin/perl
#complete -G '*.bak'
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And awk to extract it:

awk 'NR == 1 {next} /^\#complete/ {print} /^[^#]/ {exit}' $filename
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Explanation of the awk:

1. NR == 1 {next}
   Skip the first record
2. /^\#complete/ {print}
   Print any lines that start with #complete
3. /^^#/ {exit}
   Stop processing when a non-comment line is reached