Custom Marketo Date Field Type: Pre-Fill Date

In an update from my original post, is there a way to pre-fill the date to a certain month? Our event is in October and when people register, it would be most beneficial to have that month pre-filled.

Previous:
I created a custom Marketo "date" field for an event registration form. Is there any way to limit what dates are actually shown? Or block specific dates from being selected in the field itself?

The reason for this option in the date field is for hotel check-in. For my company's upcoming event, our attendees may wish to extend their stay, but if the hotel is sold out on a particular night, it'd help to have that date unavailable to select.