How can I insulate pex pipes that have supports at every joist?
Insulation won't make hot water come faster

When you open the valve initially, the hot water pipe is full of cool water, because it cooled off.  

Pipe insulation won't stop the cool-off, just slow it down a little, not enough to matter unless you are following someone else into the shower.  After even 20 minutes of disuse, the water in the pipe will cool significantly and you'll have to start over.  Start what over? 

Out, darned pipe!

The pipe is now (at best) a very tall piston full of cool water, and the hot water entering from the heater must plunger the cold water out, via the faucet.   The time this takes is determined by VolumeOfPipe / FlowRate.  For instance if the pipe holds a gallon of water and flow rate is 4 gallons-per-minute, it'll take 1/4 minute or 15 seconds. 

How much volume does a pipe hold?   That is Length * 3.1416 * Radius * Radius.  The important part is radius is squared, which makes it an extremely potent factor.  Double pipe diameter, volume quadruples, and so does delay. 

So what happens when a deluxe-minded homeowner decides to increase pipe diameter "to be fancy"?  Exactly. 

Options

One is to downsize your hot water pipe volume as much as possible. Will 3/8" pipe give a workable flow?  You have 2 redundant runs, but that might be better - each one has its own dedicated "plunger" of cool water to purge, but the lines would be able to be smaller, so less delay. 

Do you have a ton of extra electrical capacity in the house?  The single best way to move hot water across a house is fat AA-8000 electrical cable supplying a tankless heater right next to the point-of-use.  In a New England home, this takes careful design because you need a lot of temperature rise. 

Do you have enough electrical or gas/venting capacity to add a second tanked heater at that end of the house? 

Or given your usage, should the main heater really be there instead?