considering that it will always be either the last friday or the penultimate friday of the year, this should work:
declare @startdate datetime='20140110'
declare @lastdayofyear datetime='20141231'
select
case datediff(WEEK,@startdate,dateadd(day,6-datepart(w,@lastdayofyear)-7,@lastdayofyear)) % 2
when 0 then
dateadd(day,datepart(w,6-@lastdayofyear)-7,@lastdayofyear)
else
dateadd(day,datepart(w,6-@lastdayofyear)-14,@lastdayofyear)
end