If the user is specifying the boot device, could you not 'teach' them to LABEL the boot device and live off something slightly more fancy (but akin to) the following:
----
while true
do
mount LABEL=root /whatever
if [ $? -eq 0 ]; then
break
fi
# do some md and lvm magic dance here
sleep 1
done
----
Your initramfs could do extra steps everytime the loop...erm...loops.
Now of course the downside is LABELing mounted devices, XFS for example, is not an easy thing to do... :-/
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