This is a really, really frustrating problem for me.
I am an admin in a research environment and we do not let users Administer their own Mac machines. Because of this administrative authentication required, I cannot roll out a combo Boot Camp + Parallels solution as I have to be there to mount and unmount disks.
Unfortunately, I only realized this limitation (nothing seems to be written about it) after rolling it out across four MacBooks. Now I have to revert them all to regular Parallels installs. What a hassle and a pain. I hope Parallels can address this issue soon.