Is there a way to dynamically update the parameter window, so I could write a simple GUI that dynamically adds or removes parameters?

What is the canonical way to create an empty OpenJSCAD object?
I have some code where I need to union() several objects, but each of them is optional.
I would like to write something like:

o = empty_object()
if (cond1) {
  o = union(o, ...)
}
if (cond2) {
  o = union(o, ...)
}
if (cond3) {
  o = union(o, ...)
}

I can probably do something like:

o = intersect(cube(), translate([0, 0, 100], cube()))

But I would rather have something more descriptive.