Sorcerers have the most expensive training costs of any pure, especially in the lore category.
Wizards get bonuses to casting some spells when their familiars are present, why not allow sorcerers to do the same with demons?
Let having a demon summoned provide a enhancive +20 demon lore ranks (plus or minus X depending on demon type, but let 20 lore be the baseline) like some Assume Aspect functions. As if the demon were giving us pointers on keeping our cloaks in line, or summoning a presence for torment, perhaps holding our hands as we shift between planes. It makes perfect sense.
Since you cannot summon a demon without another demon being present, you couldn’t use this to boost your own demon summoning directly. Also, by adding enhancive lore ranks you’re making implementation easier by just making the spell produce an enhancive effect, rather than coding in new hooks in all demonology using skills or spells.
I would also consider grouping bonuses. You gain have the ranks of the bonus of any sorcerer you are grouped with. This would encourage player interaction, and help when people are teaching others how to use demons. If a young sorcerer is having trouble summoning, joining with an older sorcerer with an existing demon (who would be, conceptally, providing pointers or assistance to the sorcerer) would help them summon.
You could also add new uncommon runes that require ungodly amounts of summoning to use, such as say 300 or 400 ranks. The only way then to complete that summoning would be to have many sorcerers join together with helper demons. Another neat group RP application.