As you have probably noticed, many soil mixes contain bits of styrofoam. This acts as an aeration additive, therefore it only makes since it would work for drainage as well. This method can take the place of a non existent drainage hole.
Many of our clients have BEAUTIFUL containers that they have always hesitated to plant because they don't have a drainage hole, but over the years we have shown them how to line and properly plant with their leftover "peanuts" (styrofoam)! So if you have a container you would love to plant, but didn't know you could...bring it to us!!!!!!!