I'm not getting access to the real match operator (m//) so I cannot supply any options

Oh yes you can. There's a way to provide options inside the regex, even for only part of the regex, by putting them between the question mark and the colon in a (?:PAT) (non-capturing parens) construct. For example, these are equivalent:

    /.*/si

    /(?si:.*)/
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For automatic help on the syntax, try print out a qr// pattern with whatever options you like.

    print qr/.*/si
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    (?si-xm:.*)
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As you can see, there are even more possibilities using this syntax: you can locally disable certain options, even if they're globally set for the whole regex, by putting a "-" in front of the list of options you want disabled. See also perlre.