@input = qw/here is some input/;
my $imfile = join "\n",@input;
open(MEMORY,'+<', \$imfile) or die "Can't open memory file: $!";
# Then use IO::Handle or open to just override STDIN.
# To be comprehensive you could check the version of perl.  If it's not high enough, you could require IO::String, to solve the problem, as well..