Good on you! We do all the lateral work on the ground with our RI and it's great.
Use a lunge cavesson and lead rope and a schooling whip. You use your hand on the rope close to the cavesson to move the head/shoulders. You use the whip very gently where your leg would go to move the quarters. From this position you should be able to go most moves.
Our regular routine before we ride is: walk 4 counts, back 4 counts, move shoulder off track and shoulder in 8 counts, push nose away from you and do a half pirouette to change direction, counter shoulder in 8 counts, push nose away to finish pirouette.
The basic commands, other than moving away from the whip where your leg goes, include to halt put your whip on top of the hind quarters and say halt. To go back turn your body flip lightly to face your horse apply pressure on the rope and waggle the whip up and down next to him while saying back.
For turn on the forehand use a cone placed in front of you for the horse to focus on, it makes it much easier.
It's addictive stuff once you start, we start in walk and the progress to trot, piaffe, half pass etc. it does wonders for their top line and flexibility and you only need to do 5 mins a day.
I have some videos I need to post from our last demo so I'll try to get them done so you can see it in practise