I built my own stand and have a 90 under my 120. Steel stand will hold the weight. If you have the room put it underneath. If not build one out of wood and paint it.
Do you have supports under you tank? I ve done this with several tanks, I just put down thick would pieces cut to fit inside and or under the stand and then set the tanks ontop of it and I have had no issues yet. I just make sure it has support first. Make sure it it can fit under the stand and does not stress your current stand and make sure there is support for the tank its self that you are adding under the stand.
my 40 barely fit under the 120's standard stand... we also braced the underside of the stands bottom to support the 40's weight ( it's runnign as a sump for the 120) on a 125 you'll have to do a custom stand 99% sure.. the 40 is as deep as the stand is. imo no safe way to do it w/out either building a custom.. or customizing a pre-fab stand quite abit.