The easiest and cheapest solution is to get heat wrap cable for your piping. If your building is anything like mine was in Chicago, the outside spigot is fed through a pipe that can be found in the basement. Even better if you put pipe insulation over the heat wrap cable. Get an outside spigot cover, plug in the heat wrap cable in the morning for a few minutes and you should be good to go. I wouldn't worry about the pipes bursting honestly If they were going to burst, they'd do it regardless of if you're using the spigot or not.
The expensive and PITA option is to get a water tank like an IBC tote. Once filled you can find "stock tank heaters" or "tank deicers" which are typically used on farms to heat the water just above freezing level for animals. You will more than likely have to use a pump to feed your PW with this option however. Personally, I use and recommend the link below. It's an on-demand pump with an adjustable pressure switch. I've had mine for a year and half and it lives inside my truck and hasn't failed me yet.
Yes, I've added hot water to the keg before to help it dissolve. It helps, but still requires a fair bit of stirring.
I figured that I'd just add some pressure to the keg and bleed the pump outlet side in order to prime it.
I actually have one of these diaphragm pumps sitting around in the garage; I might try that.
$80 for the pump on amazon, Foxx sells them for way more than they're worth. but you can get submersible ones for even cheaper.
Sorry for the late reply, I'm probably the only one who checks this sub. I have a double IBC tote setup, with this pump: https://www.amazon.com/Shurflo-2088-594-154-2088-Diaphragm-Industrial/dp/B0001FAA5Y/ref=sr_1_fkmr2_1?ie=UTF8&qid=1499722510&sr=8-1-fkmr2&keywords=in-line+water+pump+shurflo
With a couple of in-line filters: this on on the pump inlet: https://www.amazon.com/SHURFLO-255-315-Swivel-Water-Strainer/dp/B002XM3IP2/ref=pd_sim_60_8?_encoding=UTF8&pd_rd_i=B002XM3IP2&pd_rd_r=YQ8Y2Y060CD2PTJX5HB0&pd_rd_w=RXwRJ&pd_rd_wg=dIo1a&psc=1&refRID=YQ8Y2Y060CD2PTJX5HB0
And this one (I think) on the IBC outlet: https://www.amazon.com/Female-Strainer-mounting-stainless-screen/dp/B00CH18YFS/ref=sr_1_1?ie=UTF8&qid=1499722741&sr=8-1&keywords=inline+strainer
I think my long hose is 100ft. Is there a lot of head? What kind of sprinkler is it? How large of an area do you want to cover?
I have a sprinkler similar to this one that works pretty well, probably covers around 12x12ft? https://www.amazon.com/Sprinkler-medium-watering-troubleshooting-Needed/dp/B01HB1NVH4/ref=sr_1_6?ie=UTF8&qid=1499722821&sr=8-6&keywords=sprinkler
I've used it with another sprinkler like this, but there are too many holes, so not enough pressure https://www.amazon.com/Gilmour-Light-Circle-Pattern-Sprinkler/dp/B000KL17BU/ref=sr_1_47?ie=UTF8&qid=1499722890&sr=8-47&keywords=sprinkler
I've used them in two areas in my yard with about an 8ft difference in head. Neither were effected much by the head difference.
At work we have 3 ~800gal cisterns for our plant nursery. We have a pump similar if not the same model as this one which we use for the normal back-and-forth style lawn sprinklers. It works great, but again very little head. I think we might be able to run two sprinklers at a time with this one. https://www.amazon.com/dp/B0002YVPSK?ref=emc_b_5_i