I presume you're using one of the track nuts to hold the removal tool to the wheel which is still encumbered with inflated tyre, then using a 12 inch adjustable (or equivalent) and pushing it down with your foot (on which you have a shoe)? Whilst holding the wheel with your hands, maybe with a wall stopping it moving forward?
If that doesn't work then you need a serious bench vice connected to a serious bench.
I presume you're using one of the track nuts to hold the removal tool to the wheel which is still encumbered with inflated tyre, then using a 12 inch adjustable (or equivalent) and pushing it down with your foot (on which you have a shoe)? Whilst holding the wheel with your hands, maybe with a wall stopping it moving forward?
If that doesn't work then you need a serious bench vice connected to a serious bench.