My guess is that you create another partition on the MicroSD, then you download the image, extract it to the new partition(it would probably be partition #3), then you need to create a new file for the bootmenu, it should look something like this I believe:

ITEM_NAME="MeeGo"
ITEM_ID="meego"
ITEM_DEVICE="${EXT_CARD}p3"
ITEM_MODULES="mbcache jbd ext3 fat vfat" //No idea about the modules needed
ITEM_FSTYPE="ext3"
ITEM_FSOPTIONS="noatime" //No idea if this does any impact either

Of course, this is just theoretically, I have no idea if this would actually work