SQL - Select Rows in a Certain Order
This is pretty clumsy but will perhaps give you some thoughts. The idea is to number the rows and pick from there using modulo:

select x from (
    select @n := @n + 1 as n, x 
    from t, ( select @n := 0 ) as dummy
) as u 
where mod(n,6) between 0 and 1 or @n = n


Edit: As observed by @hassansin @n will have the value of the last n. Therefore the union of the last n can be replaced with the predicate @n = n