I saw this post and I too was looking for a way to do this in Cura 15.04.3 but the option to change infill line width was not available. I decided to try the Beta 15.09.91 (windows 64) just to see what it was about, and to my surprise, there it was.
I wanted to use the infill as a truss system and remove the top and bottom layers to create an open structure. I could do this in the model but it's much easier to let the infill do it for me. This won't be structurally accurate as I do not have control to put the truss exactly at critical stress points in the structure, but it will look cool
I must say, I have only had my UM2 for 2 weeks but I can tell already that this 3d printing is going to consume my every available moment just as programming did back in the 1990's and you can bet that you will see me on the forum and the community quite often in the future.
I have not tried yet but I should be able to orient the model on the build plate to create diagonal or linear infill. Let me see if I can load some pics.
http://s1379.photobucket.com/user/rlolley/media/infill03_zpsej9ksuaw.jpg.html?sort=3&o=0
http://s1379.photobucket.com/user/rlolley/media/infill02_zps5xuohybu.jpg.html?sort=3&o=1
The beta does crash sometimes, but it's not a full crash, it gets to the "windows must close this program" but I just hit the red x and it goes away.
Robert