Even after depositing $40,000 into your account your net worth is still $40,000. The fact that your funds are not in a bank but in a brokerage account is insignificant for your net worth.
Invest your cash in dvy. This is a solid investment with 3% dividend. It can nicely substitute real estate for some time.
http://finance.yahoo.com/q/bc?s=DVY&t=5y&l=on&z=m&q=l&c=
I always felt that FCMs have more credibility than IBs since in my mind they are backbone of the business. Besides I believe most of the time IBs instruct you to deposit funds to their respective FCM accounts anyway.