Trick fruit trees into flowering later in the spring
You are on the right track, but snow is the wrong way.  When the snow is around it insulates the ground.  Soil surface temps stabilize at close to freezing.

Instead, do the reverse.  Remove, or firmly pack the snow.  Do so about 1.5 times the dripline radius.  (If the dripline is 10 feet from the trunk, pack out to 15.)

This allows the ground to freeze deeper.  However see other answers.  I'm not nearly as confident about this now.

Now once melt starts in earnest, cover the ground with a couple of layers of the insulated tarps used by contractors to pour concrete in freezing conditions.  This will keep the ground cold, both by reflection (most tarps of white) and by insulation, and by wind reduction.  This should slowdown bud break by at least a week, and more likely two weeks.



For a single tree, you may be able to do protection with an oscillating sprinkler (for a big tree) or a impact rotary.  Key thing with these is to start them before the temperature gets down to freezing.  The initial few minutes while it's working with dry air you can get supercooled droplets that kill your buds instantly.   Start the sprinkler when the temps are about +6



A third way that may help is to graft onto a different root stock.  The russians work with pear on cotoneaster.  This dwarfs the pear strongly, but also forces it into dormancy earlier.  I haven't read what it does to bud break, but given that pears also tend to be early bloomers, it must help.  These interspecies grafts are working in Siberia in zone 2.  

Look at using prunus that tend to go into dormancy early in the fall.  



Another way to experiment with would be to keep them a bit thirsty in the fall.  If the roots are slightly dehydrated, then the first moisture they get in spring will be used to rehydrate.  This may delay bud break by a day or two.



Some trees do their budding on reserves in the bud and twig itself.  I see this some years when a winter has killed roots.  The leaves break bud, inflate about to about 1/4 size, then wither.  For these guys it's a matter of enough degree days or the day length on the bud itself.

If it's degree days, you may be able to stretch things out by making the tree lighter coloured.  Many people spray dormant oil in late winter anyway.  By adding some cheap latex paint to the dormant oil mix, you lighten the colour of the twig, and so reduce sun warming.