You could mash w/out the smoked malt, run-off whatever first runnings are needed for 5 gallons (top-off the high gravity runnings with water), then add the smoked malt to the mash & rest for a bit (20 minutes?) then run-off the rest to another kettle. Another option is to not mash the smoked malt but steep it in your wort or mini-mash it and add that runnings to the wort. I'm guessing the first option might a bit easier to formulate and control than the second. Have fun with it!