From what I gather.
Add the small base layout in the designer (320x480)
then uncomment the AutoScaleAll in the designer.
AutoScaleRate = .3 or similar value can be added before calling AutoScaleAll to adjust/tweak the size.
My scenario was different. I didn't start with such a small view. Still trying to see how to best get it working right.
It's in the Designer Scripts tab of the designer