Yes. Go to Options and enter (or copy/paste) the full URL of the page into the first field of the “How to Block” section of the relevant block set.

Important: Be careful to ensure that your custom blocking page isn’t also on the block list, otherwise you will cause a blocking loop that threatens to tear a hole in the fabric of spacetime and destroy the universe — or maybe just cause your browser to hang. To avoid this problem, add the host of the blocking page as an exception. For example, if you want to block *.com and your blocking page is hosted on www.mysite.com, add +mysite.com to the block list.