I can indeed confirm that the 2nd phone on the plan method works.
It obviously works best if there is a phone on the plan already WITHOUT unlimited data. The employee simply upgrades the line that doesn't have unlimited data on it, then moves the new phone onto your line.
Another option if there is no other line on your plan already is to create a line, spend the 300$ on the phone, cancel the line for what I believe is another 350$, and then 10$ a month for 2 years for another $240. In the end spending 890$ and a huge headache.
The last option is buying it out right, for 900$.
Though there is one more option, never tested it so YMMV on everything from legality to it actually working, but bare with me on my thinking. Any time, I think any time at least, existing plans can be moved from one account onto another and on an account to their own account without affecting the plan itself. So potentially this could mean that you could move someone onto your account or you could move onto someone's account and upgrade their line with your upgrade and just simply move the phone back onto your line. Then potentially separate the accounts again.
The problem with that last one is, like I said, I've never tested it nor looked to far into it. So problems you could run in to is there actually is a waiting time to move accounts around like that. As in I know you can basically go on and off a family plan, I just don't know if you can do them in quick successions. A family plan is generally cheaper anyways, but you need someone willing to jump on that ship as well. Remember, family plan doesn't have to be family members. I'm pretty sure it doesn't put any restrictions on either line, such as upgrade eligibility, but again I don't know.
IF you do decide to try the very last option, I'm unsure if it should be announced to the world or not. I have a feeling Verizon would find a way to squash the whole thing from working if it does heh.