Sure, its possible, but is generally more complex than it's worth. You could try:

# %params defined elsewhere, holding CGI input data
open(OUT, '|-', '/path/to/cgi') or die $!;
foreach my $key (keys %params) { 
    print OUT "$key=$params{$key}\n";
}
close(OUT);
[download]

It's generally easier to load the second CGI's subroutines into a module and use them from there. The example above will work in one simple (though common) case and fail in a thousand others.

----
I wanted to explore how Perl's closures can be manipulated, and ended up creating an object system by accident.
-- Schemer

Note: All code is untested, unless otherwise stated