Jump starting directly from solenoid

[yank]

I'm looking at wiring in a lead to the starter side of the solenoid on my RS Venture to make it easier to jump the starter directly. I've been running a lithium battery for a few years now and it starts fine most of the time but when the temps hit -20's below it takes a lot of cranking and I don't want to stress the starter. I know it's bad to jump lithium batteries since surges in current below freezing can cause plating and shorten their life so I thought I could bypass the battery altogether and use a warm jump pack on the lead to the starter and grounded to the frame to crank it on really cold mornings. Has anyone tried this? Make sense?