Grounding pups to pots ... plastic??

I just found out about Bourns pots and that they are distributed by Mouser. I've been told they are very good and worth the extra buck or two. The thing is, they are built with a sealed plastic case. In the past I had grounded the neck and bridge pickup leads to the back of the volume pot. (see the stewmac diagram link below)

http://www.stewmac.com/freeinfo/i-2000/2000_2.gif

I can't connect wires to plastic. Any suggestions. Thanks in advance.

C.B. Gitty sells Bourns pots that have a metal casing.
https://www.cbgitty.com/cubecart/guitar-electronics/potentiometers-pots-.html

The pots with plastic casing have to have some ground solder point somewhere, no?

I assume you are talking about the blue ones like this?
http://www.mouser.com/ProductDetail/Bourns/82A1D-Z28-BA0-255L/?qs=reTc4FnE8%252bUoeYKBJI7R0QEhtFBezHamsIsB3eNyXE 8%3d

If you read the datasheet, they come with a solder lug washer. Basically, that is your grounding point. I sometimes do that anyway, because soldering to the back of pots is a GREAT way to fry them.

EDIT:
Sweet holy hell. I just looked at the price of these things. 16 bucks?!?! Not worth the 8x upcharge.