Cheikh:
Depending on the exact conditions, there are a few options:
1. Convert to Morph (as you said)
2. Replicate the deck profile in the Profile Manager and use it with the Beam tool with assigned slope (copy the profile from the Section window and paste into the Profile Manager), all end cuts will be vertical
3. Add parameter for cross slope to the Object (requires GDL scripting)
HTH,
David