Yes, yes you can. Just make sure that the other member is willing to give up their upgrade.
We did something like this, but not really on purpose. My brother-in-law got back from Iraq, but had already used his upgrade shortly before leaving...for an LG Dare. He didn't like the Dare, so when he returned he stole my wife's upgrade for something different. He just swapped the phone numbers between the two devices.
When it came time for her to get a new phone, he paid the $9/mo to add a brand new line to our family plan (cheaper than buying the new phone outright), she purchased her Eris, then swapped the numbers back. Now we have a spare activated phone...for really no reason at all. It was just cheaper than paying full retail for the phone.
So yes, Verizon is fine with this sort of thing. They don't really care who uses what device, just that the contract for that person gets extended.
