Yes that lack of off line charging for some custom ROMS almost made me send my phone in to repair. This was made worse by the fact that the build of CM I was on didn't allow you to boot into recovery (you could only reboot into recovery)
What I did.
Take the back cover of and have a pen ready so that you can use the hard power off function.
Prep your computer with flashtool open, drivers installed etc. – so that you can flash doom kernel as quickly as possible (you may only have 20 or so seconds).
1. Charge your dead phone, but AS SOON as begins to power up use your pen to power it down until it vibrates three times,
2. At this point you’ll hopefully have enough charge to enter fastboot mode, if not repeat stage 1. you may have to repeat stage 1. three or four times. If yes, flash doom kernel – do it quickly.
3. Go back to stage 1. But instead of powering off, see if you can boot in to CWM recovery, because the SP can be charged in CWM – if you can get into CWM all is good.