You know, some methods of installing Linux use a utility to shrink your Primary DOS partition to make room for another partition in which you stick Linux.
Given that a DOS-type of partition is defined in the Master Boot Record (MBR), and the formatting within that partition is defined in the File Allocation Table (FAT), then alterations to those are simply performed to shrink the partition. It leaves behind abandoned, but formatted space on the hard disk that the next partitioning software simply grabs like nothing was there in the first place.
To expand the partition, all one would need to do is a little more work; you'd make similar alterations to the MBR and FAT, but you'd have to format the space inside the expanded partition (setting up logical sectors) since you can't trust what was on that space before. I've never heard of this being performed, but it should work in principle.
Has anyone heard of a program doing this kind of thing, for any formatting?