This works best for ground floor apartments or conservatories adjacent to a garden.
Using hardwood, construct an above-ground, open-topped passageway that traverses your lawn in and covers all the locations birds like to gather. Line the walls of the passageway with copper, and drill holes through
the copper and hardwood on the floor to allow for drainage.
The passage should be constructed as a loop and fairly narrow: not much wider then a hedgehog. One section of this passageway runs just underneath your conservatory or ground floor apartment. An opening is cut through the floor of this interior room, someplace convenient; for instance, near a desk, table, or bathtub. This opening has a cover with a convenient handle.
Near this opening is a plastic bin full of rolled oatmeal.
Find hedgehogs, and place them in in the passageway. Aim them all in the same direction. They will then shamble out, around your yard, and eventually back towards your apartment.
At night, ensure the cover is placed over the opening in your floor. In the mornings, the hedgehogs will have grown drowsy and will have headed towards the darkest and warmest place on the the passageway -- the underground accessable insertion beneath your house.
Remove the cover, take a handful of oatmeal and sprinkle it liberally over the hedgehogs, and then push them one at a time along the passageway until they are outdoors.
Once outdoors, they will be in the light, and since they are facing forwards, they will need to make a complete circuit before they can return to the darkness and warmth of the covered section of the passageway.
Halfway through the circuit they should be in the birds favorite location. The birds will gather, and begin to peck at the oatmeal. The hedgehogs will instinctively halt movement, and allow for simple and convenient oatmeal consumption.
When the birds are finished, the hedgehogs will return to the underground passage (or magazine), ready for either another load of oatmeal, or if you need to go to work, a nap.
Partial automation via levers could also be applied for automatic oatmeal distribution and more sanitary hedgehog nudging, for people in a hurry to have breakfast.