Just have it so you pick any 3 Cantrips from non-warlock lists and Deepened Pact is any 3 spells from non-warlock lists (Up to 3rd level).
Have Book of Ancient Secrets invocation give another 3 spells from non-warlock lists (Up to 4th level).
Provides a lot of flexibility for the class with a quasi-Bard type spell choice but with the flavour of Warlock and their limited spell castings (They're not full casters that sling dozens of spells every fight)
