I don't believe you can.

What you CAN do is send the information as PATH_INFO, by putting it in the SSI directive thusly-

<!--#exec cmd="/cgi-bin/test.cgi/hi" -->
[download]

and then picking it up in your script via the PATH_INFO environment variable- either

my $var=$ENV{PATH_INFO};
[download]

or

use CGI;
my $q=CGI->new();
my $var=$q->path_info();
[download]

either way, you'll have "/hi" in $var.

Cheers!

Update
While I'm pretty sure my version would work, merlyn's answer is (<sarcasm>surprisingly</sarcasm>) the more appropriate one.

Update #2:
Umm. . .You can call off the dogs. The "sarcasm" is because merlyn is right, and I'm not surprised.

-Any sufficiently advanced technology is
indistinguishable from doubletalk.