Yes, Yes you can.
App made by OwnZ joO
Original research by Neodos
Research simplyfied by Yamagushi

How-to;
Step one, open your map in Entity and build in the included MACH. Close Entity
Step two, Open I Can Has Squares. Open you map.
Step three, scroll down to and select "scenarios\multi\yamagushi\1x1x1box\1x1x1box"
Step four, Enter the Length Width and Height of the intended size.
Step five, Click Save.
Step Six(Optional), If you need to make more squares you will need to Duplicate and relink the mach, hlmt, coll, mode, and phmo(shad and bitm optional but if u want a skin recommended). The new MODE, PHMO, and COLL tags MUST have the same names as each other! If they do not all have the same tag names this app will not detect them properly!
Thats all there is too it. Enjoy.
Download: http://www.megaupload.com/?d=5NCQYUKC
Like Most tags, extract the H2Tags Folder to C:/.
The Program can go anywhere.