Events + : Limit registration time frame AND/OR force payment before switching to "I'm att

I was wondering if there was a way in Events + to limit the time frame for registration. For instance not later than 2 hours before the beginning of the event, since there is no way to check if an attending user has payed online when he has clicked "I'm attending" one hour before...
The ideal configuration would be to force a user to pay before his status is switched to "I'm attending". I was thinking of something like that :
- If it's a free event, the visitor has the choice between "no" or "I'm attending"
- if it's a paying event, the visitor has the choice between "no" or "pay for the event". Then, when he has payed, his status switches to "I'm attending"
How would that be possible?
Thank you very much in advance