First, I recommend you take a look at my answer to another question about photographing the moon here:
Best Settings for Nighttime Moon Photos
As for your specific question, it would probably be fairly difficult to get two shots that you could merge together without a tracking mount. As such, my first recommendation is to either buy an equatorial tracking mount, or if you have a friend who has one, see if you can borrow it. With a tracking mount, you should be able to get the necessary exposures at low ISO without any blur from the motion of the moon, which should result in a decent combination.
If you do not have access to a tracking mount, the best I can say is use the chart from my other answer linked above, and try to keep your exposure times as minimal as possible. A camera with very good high-ISO performance will make it easier to get a shot of earthglow with a short exposure, without losing too much detail. You might want to use ISO 3200 if you have it. Noise is a real moon detail killer, since your signal-to-noise ratio is pretty low to start with. Using higher ISO's and keeping exposure time faster than 1/15th of a second should do it, but you will experience some problems with noise.