What was said above.
If you have issues with that, though, yes, you can. I did that with my wifes phone.
Simply order it on his line. When it comes you'll have to activate it real fast on his line per their upgrade policy. Then just change the MEID back online or just call up CS and tell them and they'll switch the MEID's so the lines are right and you're set to go.
Only takes a few mins.