I’ll try to picture as best as possible.
I have a Wizard 3 and Master Specialist 1.
As a Wizard I have the following saves:
+1 +1 +3
as Master Specialist on 1st level I get:
0 0 +2
So I simply add the +2 to the Will Save?
It seems like “cheating”, as a normal Wizard would have 2 points less on saving throws by level 5.