Easy, first add whole days, then add the remaining ms. There are 86,400,000 milliseconds in a day.
declare @unixTS bigint
set @unixTS = 1359016610667
select dateadd(ms, @unixTS%(3600*24*1000),
dateadd(day, @unixTS/(3600*24*1000), '1970-01-01 00:00:00.0')
)
The result is 2013-01-24 08:36:50.667