They are forced into main::, but they are global. You can abuse this by starting your string with a control character: ${^Foo} is also forced into main::. (it's actually ${"\cFoo"})

++ vs lbh qrpbqrq guvf hfvat n ge va Crey :)
Nabgure bar vs lbh qvq fb jvgubhg ernqvat n znahny svefg.
-- vs lbh hfrq OFQ pnrfne ;)
    - Whreq