I agree with the "solution" proposed by Kieth Barrow. It's you're really abusing the GUID field by doing this.
That being said you have a few options easier than what you're trying to do. How many records are do you need to uniquely identify? Chances are you can use BigInt which allows numbers between -9,223,372,036,854,775,808 and 9,223,372,036,854,775,807.
This table definition would allow for 18,446,744,073,709,551,615 unique keys.
Create table Test (
Key bigint identity(-9223372036854775808, 1)
)
You could use decimal which would allows -10e+38 to 10e+38
create table Test (
Key test1 decimal(38,0) identity(-10000000000000000000000000000000000000,1)
)
That would give you 2e+38 values, which is still a little short of the ~3.4e+38 values you could have with a guid, but I'd be shocked if you need that many.
2e+38 = 2 Undecillion = 20,000,000,000,000,000,000,000,000,000,000,000,000