Since B::Deparse can do it, I suppose it's only a matter of how to access the optree and not if it's possible at all.

lanx@nc10-ubuntu:~$ perl -MO=Deparse 
package TST;
our $var;
package main;

print $var
__END__
package TST;
our $var;
package main;
print $TST::var;
[download]

AT least this works w/o parsing all STASHes.