Fair calls - I'll check on them. I also wonder if the failure of setting LD_LIBRARY_PATH isn't because of what diotalevi said, which would make it true for any *nix, yes? Meaning that the truth I'm slowly reconciling myself to is that I just can't do this within Perl only. Ah well, I'll live. Thanks.
I think what diotalevi says is true, but I think there is still a Perl solution. I think the solution moritz gives below would work (using exec). It's very similar to what's in the link in my note above. I say all this without having tried it, of course.