Default A Sum Into Else

I find myself coding the following quite often:

Code:
SELECT M.District,
SUM(case when P.PropType = 'T' or M.Status = 'SA' then
V.CurrentTaxable else 0 end),
SUM(case when SUBSTRING(P.Code,1,1) = 'P' then
V.CurrentTaxable else 0 end),
SUM(case when P.PropType <> 'T' and M.Status <> 'SA' and SUBSTRING(P.Code,1,1) <> 0 then
V.CurrentTaxable else 0 end)

[code]...

In other words, I am trying to sum 1 variable into 3 categories depending upon certain conditions. I have to explicitly negate all the conditions from the first 2 SUM's to simulate a default ending else condition. Is there any construct in SQL that will me to do the last SUM if the first 2 SUM's fail without all the negation conditions?