I wrote a macro based in excel that creates spiral stairways for storage tanks & ran into the exact problem you are describing. The resulting helix was beyond our shops fabricating tolerances. They would never have fit together in the field. The only solution is to drive the microstation helix tool. It works fine, but is slower than the vba helix code. Be sure to send explicit data to each of the tools settings, else it could use an existing data already present in the dialog box. Also, I could not get it to place the helix at the start azimuth I wanted, so I simply rotated it with some extra code.
I also found it was easier to copy the original helix the correct depth of the stringer & then skin a surface between them to create the surface than to extrude a shape, as I had issues with the profile twisting as it progressed along the helix. Dont forget to offset some helix copies for your handrails as well. You can get it to work, it will just take more coding than it should have.
Do as Jon suggests and record a macro while changing all the settings. It does record all the necessary key strokes you will need.