The PIX will not redirect. It is a firewall, not a router.
If you can't set the clients to connect directly to the spoke sites, which would probably be the easiest solution, you could investigate the possibility of bouncing the clients off a router on the inside of the hub pix.
If there is a big enough user license on the 501's set vpngroup statements there for direct connection from clients. Remember, there is a limit of 5 concurrent vpn connections to a 501.
