*unsigned* 32-bit Column Type?

I need to stored lots of unsigned 32-bit values. (I'm actually storing IPv4 addresses). These values will frequently exceed 2^31 but never exceed 2^32

My options are:

Use bigint. This is undesirable since this wastes 32-bits of space for every value.
Use int and use the negative value range to get full 32-bits worth of data. In C, it is easy and fast to cast a signed -1 to an unsigned 2^32-1. In SQL, it will be more expensive: Must cast to 64-bit and if val < 0 then val = 2^32 + val.


Is there a better alternative?

Is there a fast (binary) way to cast a value > 2^31 to a negative signed value?

DECLARE @value BIGINT
SET @value = 3000000000

SELECT CONVERT(INT, @value) -- causes error
SELECT CAST(@value AS INT) -- causes error