Calculate sum of different expense types and display the value in a piechart

Hello, 

I was wondering, is there any way to combine/sum f few expense types and display that sum as a wedge in a piechart. I need to sum up a few different expense types and show those against one different expense type. So 2 wedges in a piechart, one of them is ths sum of a few expense types and the other is just one.