Hi Hervé,
Thanks for contacting us. At the moment I'm afraid RailClone can't generate an array based solely on a surface. As you've mentioned you can however use a clipping spline to automatically generate the size of an array and remove the window apertures. To create these splines you might find the following steps help speed things up:
If each facade is a single multi sided polygon:* Go to
Polygon sub object level
* Select a facade
* Convert the face selection to edges by holding down Ctrl and clicking on Edge mode

* Click
Create Shape from Selection and set the Shape Type to Linear

You should now have a boundary spline
If a facade is made from more than one poly you need to follow a slightly different procedure to generate the boundary splines. * Go to Polygon sub object level
* Turn on
Selection > By Angle to easily pick all the polygons on a facade
* Select a facade
* From the Ribbon tools hold down Shift and click
Modify Selection > Outline
* Click
Create Shape from Selection and set the Shape Type to Linear

You may also find the on
Clipping Splines chapter from our Next Steps with RailClone guide helpful.
I hope that helps, please let me know if you have further questions.
Many thanks,
Paul