The idea of a riser sounds intriguing. A few years back, we had to isolate a sensitive microscope from a factory floor. We used something similar to the items in the link below. I couldn't find the exact pucks we used, but these look close.
You have to calculate for loading. Too heavy or too light and they don't work. The ones we used were advertised to isolate down to 4hz, but we measured it about 10hz. It was good enough.
Just a thought to go along with B_H's idea.