Per Product Signed Up Date/New User Count

We have users that can access multiple products. They can also onboard to these different products on different days/timelines. Such as, they could be a user of one product for a year then pick up another product of ours. We use the same User ID for the user as they adopt more of our products. 
The issue that we are running into is that Gainsight PX only captures "Signed Up Date"  once, for the first time that the user is initially seen. So we have no way to know when that user's first session was in a new product. We are going to overcome this with a custom field for "Product XYZ Sign Up". 
This however does not give easy reporting capability as there is no analytics report type that does over time. The default widgets for "New User" only reference the "Signed Up Date" field. Making it impossible to have multiple date fields that can be reported on. 
Is there a way to get the “New User” graph to be product specific? Is there anyway to even visualize the new custom field that we populate with a per-product signup date? I have yet to refine this issue into a clear enhancement request. But it is clear that this is blocking us from seeing the adoption of new products.