I have same situation as you, live in CA and want to drive in the Sierras in the winter. To comply with CA law, need a chains / cables solution for the vehicle. I had been in touch with the Volt team and was offered this advice:
"have some information regarding the Volt tire and chain question.
As you are well aware, the VOLT officially is considered "NON-chainable" as indicated in the owner's manual. However, for Europe, we recommend the following tire size and rim size: 205/60R16 96 XL or "extra-load" rated tire
The correct rim dimensions are: 16 x 6 1/2 J with 41mm offset. This tire is the chainable tire size in Europe, and therefore, will work for the Volt in the USA. If chains are to be used the vehicle must have 16" wheels and tires and GM offers a 16" wheel that will work.
We use a steel wheel 16 x 6.5 ( from a CRUZE) with a Winter Tire of either
205/60R16 96 H XL Michelin Alpin A4
205/60R16 96 H XL Goodyear UG7+"
I just recently got this info. So have not yet priced out the solution. Or tried it on snow.
Thanks,
Art