In the past I have called my Investment Consultant at Scottrade and they have entered the trade for me right over the phone. This assumes you have an amount in your account that sufficiently exceeds your trade request.
TD allows me to buy before the funds clear. I think that the amount is based on how much you have in your account. Many times I will purchase stocks and then transfer the money immediately afterwards. The transfer usually doesn’t clear for a day or so. I have never have been charged interest or penalty for this.