how focus NEX lenses to infinity at night? (with nothing visible)

I've been trying to do more night photography with the Nex-5n since I got the remote/can do bulb setting for extended exposures. I'm normally in the cold snow/wind outdoors snow camping or mountaineering. Not in the comfort of a balcony over-looking a city or something like that.

I keep running into a problem with having out of focus night-shots even when I try my best.

1) Will shine a headlamp or light on foreground item and use peaking to get it in focus

• this sometimes helps, but even then is difficult. I'm not actually seeing any item in focus, but merely when there is the most peaking-color, as its too dark, my illumination too weak.

2) does not help if I am shooting stars at all

-I've attempted to shoot with the most peaking contrast on a bright star but it is almost like trying to focus on 'noise'---kind of futile.

3) I've occasionally bumped the ISO to 25,000 while trying to focus in an attempt to have the camera pick up a bit more while framing the shot/getting in focus. maybe helps a little but not really. Once I think I have it in focus I bring it back down to ISO100

is my only solution a manual lens (ie not a NEX mount) that has focus ring that is marked?