On my lastest build came up with a new way (for me anyway) to hold LE sheeting in place while gluing.  Works great because it puts pressure on the sheeting to get a good tight fit up against the LE on the wings that use a diamond shape LE stock.  No pins or tape required.  Just the weight of the aluminum channel is all thats needed.   This is for the joint at the edge of sheeting where it buts up against the LE.  I use wood glue, let it dry for about an hour, then spray a water mist on outside of sheeting only and its real easy to curve the sheet down to glue aft end to spar.  The aluminun "T" channel works good for lots of other gluing operations.  You can get them from any of the online woodworking suppliers.

The aluminum T-tracks are typically 1/2 x 3/4.  
Rockler Woodworking is one of many sources:  http://www.rockler.com/product.cfm?page=21967&rrt=1

The aluminum angle that its resting against is 1 x 2.5 x 1/8".   That should be a local hardware item.

I should have noted in original post that the typical diamond LE wing design uses a 1/4" balsa square and the sheeting lays on top of it.  In my case I replaced the 1/4" with a 3/8" square and the sheeting buts against the back of the LE square.
Thats why I had to come up with a method to provide a force downward at a 45° angle.