you need to create an metadata table (say... customer_id, table name , column_name )which wil contain column list per customer level (assuming every customer will have definite columns list )
then once any customer calls ... the related columns will get picked up and used.
this is small output/suggestion based on your small input/details:-D
-------Bhuvnesh----------
I work only to learn Sql Server...though my company pays me for getting their stuff done;-)