My guesses are:

sub thisoutine {
    PRE_CODE();
    thisroutine() and do {
    CONTINUE();
    };
}
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or

sub thisroutine {
    PRE_CODE();
    unless (thatroutine()) {
    CONTINUE();
    }
}
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However, with the latter one, you should be aware of a certain optimization bug described in Re^3: A cleaner way of scoping variables (Update: fixed link) which may cause that the return value of thatroutine is not returned it thatroutine() is a compile-time constant. Also, do not replace unless ( with if (! or if (not, as those would cause the subroutine to return the result of !thatroutine() if thatroutine returns true.