What are you trying to do? What is your use case where it is necessary to interpret the contents of an interpolating string constant differently when it's going to be passed to the shell vs. when it's not, but for which it's not adequate simply to do

sub my_qx {
    my $string = shift;
    # do stuff to $string, like you would in your "overload"
    return qx{$string};
}

my $variable = my_qx q{stuff};
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?