Would lager yeast help?

I have a Dead Guy Clone that has finished high (1.020), due to my helper thinking 160 was close enough to 157 and tastes too sweet for my liking. It has been in the primary for 4 weeks so I am sure the Pacman have finished what they can. I have read that lager yeast can ferment some sugar that is unfermentable for ale yeast. If this is true if I pitched some lager yeast and kept it at the correct temperature would it reduce the FG?

Won't help. Although lager yeast is unique in that it can ferment a particular sugar molecule that ale yeasts can't, your beer doesn't have enough of that sugar to make a difference.

1.020 doesn't sound that bad. If it seems sweet, boil half ounce of hops for 30min and add. Repeat if necessary.

Thanks, maybe cold and carbonated it will taste less sweet

dry hopping might help add something to balance the sweeter flavor too.