I would use the following alternative recommendation: Instead of using the project field for business, I would create a new custom field "business" and enter the business name for each project in each one. Then modify the project view(s) so that they are grouped by "business". This should give you most of what you want. You'll need to include the business field in the project view and will need to drag and drop each project into the correct business group....
I do this with my focus areas. I found it was sufficient to assign the field only for project type outlook tasks and not Next Actions (@Calls, etc.)
It is a bit of a hack, but I'm affraid if you have multiple projects going for many businesses, then you'll overload the outlook item with too much.
Subprojects are okay for splitting really large projects into blocks but they really only allow you to create a label.