Rather than blasting the entire glob, couldn't you just blast away the CV* inside the glob.

#!/usr/bin/perl -w

use Inline C;
use Devel::Peek;
sub foo{1;}
*{main::Foo} = \&foo;

print Dump *Foo;
clear_cv(*Foo);
print Dump *Foo;
__END__
__C__

void
clear_cv(SV* gv) {
  if(SvTYPE(gv) == SVt_PVGV) {
      GvCV(gv) = Nullcv;
  }
}
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