Yes you have to make a premium account. Model accounts cannot tip. The tokens you receive on your model account are automatically paid out to you, they don't sit on your account/don't have to be converted like on CB.
You'll likely run into a snag when you try to purchase tokens on the premium account, though, since their system will recognize it as a duplicate account (same IP address, same contact information) so you'll need to send an email letting them know what's up when that happens.
Lots of us have premium accounts. Many models do not allow other model accounts into our live chat room because they are a distraction and many have ill intentions, so going in on a premium name that is not directly indicating that you're a model is best. (You can always tell the model privately who you are, just no need to make a big hubbub about it in the room for all other viewers to see.