This is not possible (by design), for security reasons.
Alternatively, you could keep a record of which item_id's are currently
"checked out" in the application scope. The application scope is shared
amongst all users on the server. Any time a user checks out an item and adds
it to their session, you could keep a record of that in the application scope.
( I would probably store a STRUCT that has item_ids as keys) Once the user
releases the item (or perhaps after a timeout period), you could remove that
item from the application scope.
If you're in a clustered CF environment, you'll probably need to use a
database table instead, but at a high level...using the very same approach.