I have seen a few posts related to this topic but have yet to find any concrete answers.
We are looking for a way to sum members when going to the base level with a where clause without seein...
If you are looking for a way to separate out which products (UD4) are consideres VAS by using the text1 field, I think you can use the attribute function on the User-defined dimensions. If you for example separate the Value added products and non-Value added products in UD5, then you can just choose the VAS member in UD5 to get the sum of your products being defined as Value Added. See print screen below
This will include all products tagged with VAS in text1 in UD4. So, only add UD5 to a column and set it to VAS. The great benefit of this is that you can actually have a product being Non-Value added product in the beginning, but then later changed to Value added product. This is because the Text1 field can change over time and be set differently for different scenario types. I use it in my own application to get my billable hours my tagging my different tasks (in UD) with billable or not-billable. Great function! Especially since the the Text fields can change over time.
I hope this helps solving your problem, even though it's a bit different than what you originally is looking for.