Best I can come up with is something like this (note, this works in Excel 2003 - might not work in 07/10, but you've haven't indicated which version you are using):
Ctrl + Space to select the source col.
Ctrl + X to cut the col.
Left Arrow or Right Arrow to move to the column you want to move the selected column to the left of.
Crtl + Space to select the target col.
Crtl + + to insert the cut cells (with thanks to variant for that useful comment!).
I'm thinking that AutoHotkey or a short macro might be a good way to achieve this.
It should be easy to record a quick Excel macro using the above set of commands, just make sure "Relative Reference" is on.