Swap plugs whenever you change Computers?
They don't sell double plugs because if you accidentally have both working - there will be problems and its likely the monitor will be ruined.
Either that or get two monitors - go to a Boot Sale and get one for about £5?
A Knight is sworn to Honour. His heart knows only Virtue. His blade defends the helpless. His might upholds the Weak. His word speaks only truth. His wrath undoes the Wicked.