Funny you should mention using the chalk bags. I am in the process of doing exactly that.

http://bicyclehobo.com/diy-bikepacking-feedbags/

My prototype was made without sewing, but this weekend I will be slicing the webbing and sewing some velcro. I think that this prototype would work, but it's a bit ugly. I got the chalk bags for $6.99 apiece.