This trick still works, in case anyone is wondering. I was able to do it a few days ago. I already had a dumbphone (in use) on my family plan, so I didn't have to actually pay extra or anything. I followed the Droid Life guide, making sure to activate the new smartphone first on the dumbphone line. I couldn't switch that line back to the dumbphone online (there was an error), but I called Verizon customer service and they did it for me instantly. Just make sure you note the device ID for the dumbphone before starting this process (it's available on Verizon's site, if you log in) - it'll make it super easy for the CS rep to switch that line back to the dumbphone if you can just tell them its device ID. After that, turn on the dumbphone, dial *228, then select option 1. That'll complete the reactivation process.
Finally, I just took the LTE SIM card out of my GNex and put it in my G2, which worked immediately and flawlessly. It's been smooth sailing from there. Verizon's site says that the contract on my smartphone line has been extended to Oct 2015, and it still lists the data as being unlimited. I'll have confirmation for sure that it'll work in the long run once the next billing period starts for me in a week or two.