Unfortunately, unlike open close has little magic and only accepts real filehandles. After quickly perusing the dox and experimenting I see nothing too promising other than a fork (with no dup or pipe) and exit.

UPDATE: Okay so here's a possibiliy, the details I'll leave to you, but it's not pretty. If you look at the symbol table (%main:: for package main) entries with value /*::.+/ seem to correspond to filehandles, this gets you a list of things to close.