I'm about to build the sill plate for our new window, a 4' x 82" monster. I plan to double plate the sill, the two boards laying flat atop each other. I have a spare 2x6 that has no other use as of yet...So my question is: Can I use the 2x6 on top of a 2x4 for my sill plate? I was thinking it might be a nice feature, a protusion just beneath the window. Any thoughts are welcome!