For what I know this is not possible, and actually I think that it is not safe to connect the same disc to two different machines in this way.
If you need to connect the same disk to more machines at the same time, the best option (for what I know) is a NAS, i.e. an external disk provided with a network connection. Connecting the NAS to a hub, you can share it among many machines.
A cheaper alternative is to get a device like this one.