I had a similar issue, but was also required to remove the decimal point where no decimal was present, here was my solution which splits the decimal into its components, and bases the number of characters it takes from the decimal point string on the length of the fraction component (without using CASE). To make matters even more interesting, my number was stored as a float without its decimals.
DECLARE @MyNum FLOAT
SET @MyNum = 700000
SELECT CAST(PARSENAME(CONVERT(NUMERIC(15,2),@MyNum/10000),2) AS VARCHAR(10))
+ SUBSTRING('.',1,LEN(REPLACE(RTRIM(REPLACE(CAST(PARSENAME(CONVERT(NUMERIC(15,2),@MyNum/10000),1) AS VARCHAR(2)),'0',' ')),' ','0')))
+ REPLACE(RTRIM(REPLACE(CAST(PARSENAME(CONVERT(NUMERIC(15,2),@MyNum/10000),1) AS VARCHAR(2)),'0',' ')),' ','0')
The result is painful, I know, but I got there, with much help from the answers above.