This might sound weird, but what about flagging Koggy's attacks as Melee?

It would probably get stuck in as his new Innate, something like-

Unnatural Geometry: Like all Voidborn, Kog'Maw extends beyond the bounds of visible space, allowing him to savage foes at impossible distances and angles. Kog'Maw's basic attack are considered Melee rather than Ranged.

Instead of spitting acid for his basic attacks (all skills would still be acid-based), he bites the air in the general direction of his target, causing a pair of jaws to manifest out of thin air and chomp them. Many of the items and masteries most attractive to Koggy greatly benefit melee champions over ranged ones. If Koggy's basic attacks counted as melee, he would be able to utilize them a little more efficiently. You could probably even tack on a healing component when basic-attacking enemy champions if Koggy still needed a pick-me-up.

And best of all, this would finally incorporate eating things into Kog's kit, which is a Lore disconnect I've been scratching my head about ever since Kog hit Live.

For added points, give him a 'nom!' sound effect for his basic attack rather than the vomiting noise.