I am not sure if I understand your question, but AFAIK you can't run WM and Android 'at the same time', you can Keep your WM on NAND and install Android on your SD, thus you don't wipe WM, then you use a program called HaRET to run Android (this unloads WM from Memory and boots Android), once you have finished with Android you can switch back to WM by just rebooting, bang, you are back to WM, nothing lost.
I don't think there is enough room to install 2 Rom's on the System Memory, thus you can't 'dual boot' (as you would on your computer) so its slightly different.
Does that make it any clearer?
║ ♥ Leona. ♥ │
Phone: Sony Xperia Pro (SIM Free) Black Model: MK16i Build: 4.1.B.0.587 Android: 4.0.4 Stock not rooted Baseband: -77 Kernel : 184.108.40.206 BL: Locked Carrier: 02
Tablet: Elonex eTouch 1000ET (ZT-180) Android: Froyo 2.2 Abtekk's Custom ROM 3.6 Rooted.
Former / Retired Phones. (1999 -> 2012)
Philps C12 (Cellnet), Motorola C520 (Orange), Nokia 6110, 6210, 6310, 7250, Sony P900, HTC Wizard (02), HTC Tytn 2, LG GW620 EVE