Not sure with mason's but I know bumbles might be another good solution.
Try to lure them into your yard.
What I would do...put a bunch of boxes up, it could be clay pots on the ground and some up on post's filled half with insulation. The drain hole would be the enter hole, close off the large opening or bury into the ground, side of a hill, expose the drain hole.
Also bird/nesting boxes, put a reducer, piece of wood with a small hole about the diameter of your thumb and screw on top.
I think it's still time to do it now,.. young queens in spring are searching for new homes.
Try different insulation,.. they also like moss!
I'm on the call list for swarm bee removal, ...got a call last year, when I went there in someone's back yard, it was a birdhouse just loaded with bumbles!
I told them how lucky they are and not to worry, ..just keep a little distant.

The kind of bee you'll want is called Peponapis pruinosa. I am unfamiliar with your location, but they reside all over the United States. http://www.fs.fed.us/wildflowers/pollinators/pollinator-of-the-month/squash_bees.shtml

Understand that most of the world's bees are ground nesters, and this species is no different. Ground nesters are one of the more difficult species to manage, so I would suggest you observe the ground nesting species in your local environment, and try to encourage them to stay by not disrupting them (tilling, spraying, covering, etc). There are reports that some ground nesting species remain for decades.

Please understand there is a difference between a 'Mason Bee' and an 'orchard bee.' The term 'mason bee' generally refers to solitary bees that use mud resources for their nesting. Some mason bees work in late summer, whereas the more common 'mason bee' bought and sold online refers to the Osmia lignaria species that works in early spring (March to June). Of course, these months depend on geographic location and elevation.

I have never tested whether or not Osmia lignaria has a 'predilection' (or preference) for cucurbits. Considering their behavior in early spring, I doubt they would visit cucurbits, as they generally prefer tree/bush flowers over ground-blooming flowers.

I assume Bombus species would work cucurbits, and they may be a more manageable choice, but from my reading and observation, Peponapis pruinosa is your squash specialist.

Here is a link that might be useful: NativeBees

Used to get them in the Garden all the time.... they liked spending nights in the squash flowers....