Using The Left Function Inside A "NOT LIKE" Comparison

Hi, I'm trying to compare 2 name fields to see if the last name of one field is found in the last name of the other field. In table A, the name is stored as LastName, FirstName. I've used the Left and InStr function to extract the last name successfully.
In Table S the name is stored as separate fields, Lastname and Firstname.

In a query I am trying to determine if the last name from table A appears in the last name field in table S

(s.lname Not Like '*Left([a.name],InStr([a.name],",")-1)*')

the problem I think I'm encountering is that I want access to see this statement as:

(s.lname NOT LIKE '*JOHNSON*') instead of searching for the Left function string

is there any way to put the value of the function in there without actually searching the function literally?

I tried [ ] and that didn't work.. any ideas? thanks!