You can’t actually cast the spells on yourself. The “spirit” has to be dis-corporeal on the astral plane and the caster has to be in Astlan using/manipulating material components, vocalizations and somatic gestures (to borrow from AD&D terminology) so someone else would have to do it.
Well you would need to redesign the spell(s). A simple time trigger sounds workable.
1. spell: Bind the Soul into Demon body (activates in 5 minutes)
2. spell: Sever the silver cord (activates in 4 minutes)
3. spell: Go to the astral plane
Obviously you would want to test those spells before trying them on yourself…