Yes, for events with the option to pre-pay for parking (not all events have the option to pre-purchase a parking pass), you can add on a parking pass to your registration until Tuesday at midnight before the event.
To add on a parking pass for US events, simply log into your account here. You’ll see your upcoming race on the right-hand side of the screen. Click “View registration,” then scroll down, and you’ll see the option to add on parking. Simply add it to your cart, and enter your payment information on the next page.
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.