For a real training of all muscle groups with a huge range of load regulation with a pair of rubber bands, you definitely cannot do it. The pretensioning of the rubber bands is also extremely important! The muscles should feel the load already at the beginning of the movement. How will you accurately adjust the pretension without a platform? Twist the bands in half? Take 2-3 bands at once? This will help in part, but inconvenient, cumbersome, small range of adjustment. You will save money, but you will lose more in efficiency and functionality.