me and my cousin are planning to have a short euro trip. I have sufficient account balance with regular income so for me everything is fine but my cousin didn't maintain the account and he withdraws full salary as soon as it comes. 
He can provide the bank statement but the point is there won't be any funds as he usually never leaves anything in the account. So in this case can I write a letter or something that I will be responsible for all his expenses. I am having enough funds to support both us.

Thanks