Define macro "StartStuff.g" or similar. Content:
M291 P"Run startup bed leveling and such?" S3 G28 G32 ...whatever...This will result in a dialog on the web console:
99d9a6c4-b46f-48ff-b57a-b4a028bae2bc-image.png
Pressing OK will result in the rest of the macro (G28 and so forth) running; pressing cancel will end the macro immediately.
Test this; when ready to have it start every time, place
M98 P'StartStuff.g"as the last line of config.g
p.s. No conditional gcode per se; this works right now, in all 2.recent and 3.recent versions of firmware, with or without a Pi.