Had both brothers in law around my house (at different times). On their laptops I used Connect To, found the network and put in the password it was set up with.
No need for them to know - type it in out of sight if necessary. Once connected, they can reconnect again and again as the connection was saved.
I suppose there will be a hack somewhere that allows them to find out the password I typed in but I'd probably notice them if they were sat outside in their car. Or am I just paranoid . . . ?