It looks like your board is pretty simple, and with a little re-routing traces and adjusting some resistors, you can make it a 1 sided board. Traces on the back, components on the top. The tricky part would be putting the pin headers in to engage the arduino headers. For that, I would use the extended length pins and put the spacer on the top of the pcb to hold them in place while soldering, then clip the excess off, pry the spacer off and add the spacer on the bottom. Make sure and have pads up top (and solder)to keep from ripping the copper traces off the bottom when you separate the shield from the arduino.