Does this combination work?
If so, what brands are you running?
http://ducatimonsterforum.org/index.php?topic=17723.0 (http://ducatimonsterforum.org/index.php?topic=17723.0)
Take a look at this post. The Ducati bag in there is designed to maintain access for the passenger pegs. The Givi system is similar.
Depending on your final setup, it is just as possible to block the passenger pegs as it would be to keep them accessible. Bags with a chop would, I imagine, make passenger access more trickier (It's a word!).