Adding to my previous comment, I think what should happen with the installer *assuming this is not already done* (I haven't installed the latest version of ubuntu yet myself) is, the user will first come to a step where he/she has a chance to change he/she's HDD and partition layout by resizing, deleting, moving, or creating/formatting a partition. Next step, after the user has already made his system the way he wants it to be, he can then decide which partition to install Grub to, assuming he opts not to install to MBR. Presto...problem solved.
Adding to my previous comment, I think what should happen with the installer *assuming this is not already done* (I haven't installed the latest version of ubuntu yet myself) is, the user will first come to a step where he/she has a chance to change he/she's HDD and partition layout by resizing, deleting, moving, or creating/formatting a partition. Next step, after the user has already made his system the way he wants it to be, he can then decide which partition to install Grub to, assuming he opts not to install to MBR. Presto...problem solved.