Transact SQL :: Multiple Columns Needs Median Calculation

I need to get the median for the 10 columns in my table. For the sake of example, I've reduced it to 2 columns. 

The code below works perfectly if i compute for only 1 column and certainly doesn't for multiple columns.

Is there a way to better handle the median computation in one pass, if multiple columns are involved?

DECLARE @tbl as table (id_n int, col1 int, col2 int)
insert into @tbl
values (1, 1, 2), (1,3, 4), (1, 5, 7), (2, 4, 7), (2, 7, 7), (2, 3, 5), (2,5, 5), (3, 1, 2), (3, 3, 5), (3, NULL,11)
select *
from @tbl
order by id_n, col1

[Code] .....