Upvote:1
I looked everywhere but couldn't find a really clear answer. I do think however, that you have to buy the ticket at the park and cannot buy online. This source for the same discount, but last year indicates:
The Disney ticket money-off deal is until 7th November 2013 on presentation of a valid Paris Visit Travel Pass at the Disney Parks ticket desk.
I found the same for 2012, so it's probable it will still be the same now.