This is a two step process:
1. Use VHDResizer to resize the partition, download here
2. Use gparted to expand the partition, download here
Details on VHDResizer (from http://vmtoolkit.com/files/folders/converters/entry87.aspx)
VhdExpand is now VhdResize.
VhdResize will resize Microsoft’s VHD files and will also convert between Fixed and Dynamic file types. This is a sector by sector copy operation from one size/type to the other and the source file remains unaltered.
VhdResize requires the Microsoft .Net 2.0 framework available via Windows Update and here.
Installation
Unzip the file to a folder of your choosing and run VhdResize.exe.