I cannot think of a way to do it the way you are describing. Hiding certain page when all is selected is not supported currently and can be confusing to the user.
Here are couple of options –
1) Straight forward – showcase both in the same page like here by having section within the portfolio page which belongs to each category ( you probably already know this way so nothing new here ) –
http://focuslabllc.com/work/katy-skelton
http://focuslabllc.com/work/uversity
2) Have a single portfolio item for a client/work and then create pages (not portfolio items) for each category – one for print design and other for website for that project and link to these pages (with a view details link from portfolio item). That way someone interested in website can navigate to this page to know more details about the project. You can have a slider or a gallery of some kind in the portfolio item which provides some screenshots of both categories so that they stay interested.
That’s pretty much what I can think of. Sorry – wish I could help more. Thanks