100% Graph with line graph on second axis - Combo Graph

[alextomlins]

Hi Guys, 

Had a request for a 100% Graph - which I've done. They would also like the actual number of transactions within that graph but i don't think the combo/bar graph will let me do that. This is the 100% graphs as it is; 

So on top of that graph we would like a line graph with second axis for sum(Transactions) line? 

Is this possible - is there an extension available for this?