Quoted from The_Dude_Abides:I've done many blades like this. By far the easiest method is to wet the sticky part well with windex just prior to installing each side. That will allow you to reposition little by little. I've used this method to install many blades by myself with playfield up. It has always worked great for me.
+1 on this approach... it can be tricky with the playfield installed but once they are wet things slide around nicely and typically go pretty quick.