I would run summoning as three different rituals, the summoning (Creatures conviction +4 + summoned creatures refresh) , the containment (ward strong enough to beat at least +4 the enemies best means of escape, which would most likly be magic or might). At this point a Summoner could attempt social combat with demon/creature to barter for what he wants. Or they could attempt a lawbreaking binding which I would either structure as a mental block against disobeying the master (Conviction/discipline +4 + duration) or as a full mental takeout which would lead to the summoned creature having its high concept changed to include 'loyal to the master'. (conviction/discipline +4 + full concequences).
I know this method is more complex than the one step methods of Sanctaphrax but it seems closer to the actual method of summoning in dresden files books, I would not let a pc design what they were summoning beyond a name and their best research to keep thing balanced.