sh scripts can only "source" sh scripts.
csh scripts can only "source" csh scripts.
Perl scripts can only "source" Perl scripts.

What we can do is have the run csh script and output its env variables in an easily parsable format. env can help us here. In fact, it can even be done without modifying the csh script — let's call it "script.csh" — using the following Perl code:

my $env = `csh -c 'source script.csh; env'`;
foreach my $line (split("\n", $env)) {
   my ($key, $val) = split('=', $line, 2);
   $ENV{$key} = $val;
}
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Updated: I simplified my post by inlining the "wrapper script" into the executed command.

Updated: Added the closing backtick that was accidently deleted.