Yes, for events with the option to pre-pay for parking, you can add on a parking pass to your registration until Tuesday at midnight before the event.
To add on your parking pass for US events, simply log into your account here. Go to your profile in the top right corner, then click “Manage Registration” under your upcoming event, then “Add Ons” along the top menu bar. From there, you’ll just need select the option you’d like, and continue to the next page for payment!
To add on a parking pass for Canadian events, simply log into your account here, click '"edit", and add on a parking pass. Then, continue to the next page for payment.