Well, one possibility isn't to use a regex, but instead to do something like:

my @word = split //, $word_to_match;
my $match = 0;
for (0 .. $#word) {
    $match = 1 && last
        if $word_to_compare eq join //, @word[0..$_];
}
print "Matched!\n" if $match;
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