Just revisiting this topic.
I was just in my personal Amex account, and noticed that you can tag your expenditures. So I created a tag called "business" and went back and tagged the last 6 months (at least, what I remember off the top of my head). Then by selecting to show spending for the year categorized by each tag, the website adds everything up for you.
Now, this feature has probably been there for 10 years and I just noticed it (and I'm sure other banks have something similar). But it looks pretty handy if you don't want to have a separate card. However, I have bought some business items at Costco, and those are all mixed up with personal items. It seems like that'd be hard to tag. For that reason, I think paying on two separate cards, one for business and one for personal, makes things a lot neater.