Filter selection plot with multiple (static) comparison lines

I would like to have an interactive plot that changes by selecting a value from a filter. I would like to have two lines for comparison that are independent of the filter. I can create a sheet with the interactive filter and I can add a sheet with the two lines for comparison but I'm having a difficult time incorporating the two.

Here are the specific details:

I have a dataset with 3 columns -> User Name, Event Date and Value (this is binary).

User Name can have null values. I created a calculated variable called Person Group that separates User Name into a "valid user" and "Null user".

plot 1 -  MONTH(Event Date) as Columns, AVG(value) as Rows with the Person Group on the color mark. This is the plot that is independent of the filter. I would like these two lines to be my comparison lines.

plot 2 - MONTH(Event Date) as Columns, AVG(value) as Rows with the User Name as a filter. This changes as I select the filter.

In order to incorporate the two I tried to create a calculated field called Ignore Filter ->  { FIXED DATETRUNC('month', [Event Date]),[Person Group]: AVG([Value])}

I was assuming that this will ignore the User Name filter all together. However, when I use this calculated field in plot 1 instead of value, as soon I drag the User Name into the filter box either the Null user line or the valid user line disappear (depending on value in the filter). So I cannot incorporate both comparison lines together with the User Name plot.

I cannot create 3 independent plots since Tableau only allows to sync 2.

Any ideas how to solve this issue?

Thank you!