Someone with knowledge in
GDL scripting could probably create a new marker (not me).
For a workaround, place your interior elevation marker with "Individually for each Interior Elevation" selected for "Marker Placement".
Use "Style 6" as your "Marker Style" (at least... that's what I have in my US Build of AC).
Draw a 2D line and manually move the markers.
Marc Corney, Architect
Red Canoe Architecture, P. A.
Mac OS 10.15.7 (Catalina) //// Mac OS 14.5 (Sonoma)
Processor: 3.6 GHz 8-Core Intel Core i9 //// Apple M2 Max
Memory: 48 GB 2667 MHz DDR4 //// 32 GB
Graphics: Radeon Pro 580X 8GB //// 12C CPU, 30C GPU
ArchiCAD 25 (5010 USA Full) //// ArchiCAD 27 (4030 USA Full)