Here is a complete dynamic SQL solution to the problem:

declare @CustCode int = 1;

declare @sql nvarchar(4000);

with cols(col) as (

select name

from sys.columns

where object_id = OBJECT_ID(N'[dbo].[myTable]')

and name <> 'CustCode'

),

collist(c) as (select ',' + QUOTENAME(col) from cols for xml path('')

),

zeros(z) as (select ',0' from cols for xml path('')

)

select @sql = 'insert into mytable (CustCode' +(select c from collist) + ')'

+ 'select ' + str(@CustCode) + (select z from zeros)

;

exec (@sql);

select * from mytable;