Handy little hook I think...

git-tfs rcheckin prepare-commit-msg hook

#!/bin/bash

branchname=`git symbolic-ref -q --short HEAD`

if [[ $branchname =~ 'tfs-.*' ]]; then
	    workitems=$(echo $branchname | sed s/tfs-//g | tr ',' ' ' )
		for workitem in $workitems;
		do
			cp $1 $1.old
			$(sed '1s/^/#git-tfs-work-item: '$workitem' associate\n/' $1.old > $1)
			let i++
		done
	    cp $1 $1.old
        $(sed '1s/^/\n\n#Automatic Git-TFS Associations\n/' $1.old > $1)
else
	exit 0
fi