No, it is not legal! The terms and conditions of the gaming provider prohibit to let others play with your account.
Actually, breaking TOC isn't against the law in most countries. You'll probably just be banned if they do have the restriction.
But why you have to wait for a longer run.
It doesn't always have to be a longer run. When you make a bet on a 1% house edge, you are expected to lose 1% of your bet. Same thing happens when you make another bet, or another one, or 500, e.t.c. You might not lose on your first bet, but you could. Going to a different site won't help. No one will be stupid enough to fall for this and have 0.1
BTC at the same time on this forum.