I'm not sure that extracting things is the right approach. Instead I'd try to replace all newlines with \n$prefix (resp. all "starts" of the string with the prefix, in REspeak):

sub prefix_print {
    # unfortunately, the local copy of $_ is necessary to be able to p
+refix_print
    # constants
    print map { my $l = $_; $l =~ s/^/$prefix/gm; $l } @_
};

prefix_print qq(foo\nbar),2,3,4
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