Is it allowed to give someone an unwanted Runescape account

Sorry, but it is against the Jagex rules of play to lend out Runescape Accounts.
That's against the Jagex rules.

It's quite possible they will recognise the sudden switch in user (via IP address or something) and ban the account anyway.

I wouldn't bother. If you are unwilling to spend the time training your own account they you won't enjoy playing much after a little while.