I did the same as you, drilled holes in a 4x4, attached to south facing wall at about 5', but didn't have good luck. I spoke with the mason bee folk at the NW Garden Show and they encouraged me to plant pieris near the house, which is one of the bees' earliest sources of food.
I also reached out to my local honey bee club to see if anyone was interested in setting up hives in my front field, but got no takers. I do have an offer from a friend's son who is a master bee keeper (whatever that might mean) and he is willing to give me a hive and some bees and instructions but he's about 8 hours away from me and I don't like honey and don't want to mess with the bees overmuch, just looking for pollinators.
