A simple idea:
Namely, Warlocks can take Reserve Feats as if they could cast any spell of up to [Eldritch Blast dice] level, and are treated as if they had a spell of that level prepared for the purposes of any Reserve Feat that they have (so 9d6 would give you a 9d6 Fiery Burst feat output and the like.)
In addition, if a Reserve Feat deals a type of damage that your Eldritch Blast could deal (say through Eldritch Essences or prestige class features), you may add the other benefits of that Invocation to the Reserve Feat's effects (so Fiery Burst would light people on fire, for example.)
A Warlock of at least 2nd level treats their Eldritch Blast as if it were the effects of a Reserve Feat for the purposes of other feats and class features, but only as long as no Blast Shapes or Eldritch Essences are applied to it.
At 7th level, they may still treat their Eldritch Blast as if it were the effects of a Reserve feat if they have either a Blast Shape or an Eldritch Essence applied to it.
At 12th level, their Eldritch Blast is always treated as if it were the effects of a Reserve Feat for the purposes of Class Features and feats.
Reserve Feat Support
More Reserve Feats
Even More Reserve Feats
The Reserve Mage