Yes, you can do this. You'll just need a summary with a key field of , and a measure field of Sum(). This new summary should not have any filter or matching restrictions applied to make sure it picks up all the data.
Thank you Olly!
It sounds easy enough, I haven't really got a chance to play around with the key field and measure field area so I guess this is my chance. lol I might be back if I can't get it to work!