If you are not allowed to market out parked pages then perhaps you should consider changing to another parking service? Because in that case you must have domains that get typein traffic or nothing is going to happen... 
I first heard that you could not do anything to get more traffic to parked domains, but I think that has changed. You are still generally not allowed to use traffic exchanges, pay to surf, or pop-ups/unders by most services.
But getting more links to your domain and even pay-per-click traffic are options with some services. The main concern you have to have is will the traffic do more than just click on a link on a parked domain? Are they really looking for something that is offered by the ads? If so then everyone is happy.

I first heard that you could not do anything to get more traffic to parked domains, but I think that has changed. You are still generally not allowed to use traffic exchanges, pay to surf, or pop-ups/unders by most services.
But getting more links to your domain and even pay-per-click traffic are options with some services. The main concern you have to have is will the traffic do more than just click on a link on a parked domain? Are they really looking for something that is offered by the ads? If so then everyone is happy.