So, I tried to start the Z after a few weeks of sitting in the cold, and it only spun a few times before the battery gave up. This, despite being on a solar battery tender (not enough prolonged sunlight, apparently. Don't have access to AC in the garage, might need to pull the battery and bring it inside for the winter...) Anyway...

I'd like to use my portable jumpstarter and get this thing nice and warmed up, so here's my question: is there anyway to do this without the rigmarole of opening up the battery compartment? Are there some remote, easy access terminals somewhere on the bike that I don't know about?

I know it's not what you asked and not everyone agrees on this but I avoid starting in winter because I think it's best to not warm up until it's ready to ride for the season. Condensation, difficult start, poor lubrication. JMHO. I love to at least hear mine run after a few months of no riding but not unless there is some other reason like maintenance. ...or maybe you have a nice heated garage.

Also, be careful about the power of the battery you start it off of. IDT a car battery is safe. ..again you prolly know but just my .02.

How old is the battery?
Pull the right side grill panel to get at the battery +cable. Take a jumper+ to that, the other -cable to the bike frame somewhere; lift the hood of the car, install the other end of the jumper cables; no running of car. Start bike up or more turn key on twice so you pump some pump into the lines. Wait till you hear it turn off in the tank. Leave the throttle alone. This is no longer a carb bike. Push starter button only. Make sure gas is in the tank.

Thanks for the tips, guys. Not sure of the age of the battery, it's the one that came with the bike when I bought it in Nov 14.

I use my portable jump starter

Short answer is no, there is no remote battery terminal. As Hub said, you'll need to pull the side cover to gain access to the battery and connect directly to the positive terminal and any unpainted spot on the frame/engine.

Probably about as much work as running an extension cord to a batter tender, or hooking up a car battery to the existing pig tails of your solar tender and let it sit for a few hours (the fully charged car batter should put a charge on your dead bike battery, just unhook it before you try starting or you'll probably blow the fuse on the pig tail).

I installed a 12v outlet on the dash of mine. I've used it to jump start mine before. I left my hand warmers on accidentally and it killed the battery. I just made a pigtail with a plug and soaked the battery with a jump lack for 15 minutes. Was enough to get it started. I mainly use the outlet to power my GPS. And I plug a tender into it to keep the battery charged at home.