Do you absolutely need to emphasise that the variable is continuous?
I'd suggest displaying version two as a stacked column graph if you can get away with it. Humans are much better at comparing area changes in one dimension rather than two at the same time.
You might be able to overlay a line graph over the stacked column graph to get the effect you want, but that is likely to be very difficult to decipher for an audience that isn't used to viewing graphs.
Realistically, if it were me, I'd use two graphs.
download bmml source – Wireframes created with Balsamiq Mockups
One line graph like your first one to show your trends over time, and a second column graph, with only one column (covering the entire date range), showing the split between the different brands.
If you're presenting to marketers, I might even shudder consider replacing the second graph with a pie chart. Since that's the format they're used to seeing when they're comparing a part-to-whole relationship.
In either case, I'd lose the vertical gridlines. They're a large part of what is making your graph hard to decipher.
For learning to present this kind of information effectively, I cannot recommend this book enough.