Producer Andrea Messina has posted a video on YouTube with a rather useful hack, showing you how to convert that old, unused keyboard into a foot controller.
In the video Andrea pulls apart the donor keyboard and maps the new foot switches to control a DAW.
Andrea glues the chunky rubber feet on top of existing keys, for more tactile foot control and states you are better off selecting the larger keys (Enter, Shift etc.) for the job.
He then goes on to show you how to map those keys to certain functions of your choice in Ableton Live. For this demo, Scene Control, Scene Launch, Stop All Clips And Scene Up and Down functions were selected.