I too tried this with an Ergodox, but the keys you want to have your symbols on are just so far away anyway. The center columns for example are quite far.
Instead I think it's better to use layers (holding down a key to change what other keys do) and place symbols close to your home row. You can even have a numpad right under your fingertips.
This is why ergonomic keyboard users are generally moving towards boards with fewer keys, not more.
Look for QMK programmable keyboards where you can do this and much more.
Holding the key labelled "OSL1" will switch the layout to the "Symbols" tab. The blue keys are dual-function, tapping them will enter the character on top, holding will turn it into the modifier key below. Finally the Gaming layer, toggled by the bottom right key on the keyboard, turns off all the special mappings and turns it into a standard QWERTY keyboard, because my muscle memory for game controls is too deeply entrenched to deal with in the middle of a fight :)
I have the same experience. I started with using all the extra keys on the Ergodox, but it was difficult reaching them, including most of the keys in the thumb area.
I have since changed the layout to mimic the altreus layout (with most of the extra keys empty), which works much better. And am waiting for my altreus from keyboard.io to arrive as the extra keys on the ergo actually cause me to miss with the pinky and hit the "empty" keys sometimes.
I too tried this with an Ergodox, but the keys you want to have your symbols on are just so far away anyway. The center columns for example are quite far.
Instead I think it's better to use layers (holding down a key to change what other keys do) and place symbols close to your home row. You can even have a numpad right under your fingertips.
This is why ergonomic keyboard users are generally moving towards boards with fewer keys, not more.
Look for QMK programmable keyboards where you can do this and much more.