I recently suggested this for the forge:
Would it be possible to change how Isidedinventory works so that if a side is not directly linked to a specific inventory slot then something linked to that side can access any slot?
And got this reply:
That's entirely up to the mod.
You'll notice the Buffer more or less works exactly like that.
In any case I don't see any reason to have sides of a block not able to do anything with pipes and whatnot, just have it how it used to be before Isidedinventory for the sides that aren't directly assigned to a specific slot. For example a normal furnace would be able to have things put into any of the side slots (besides the right) as well as being taken out. You might not get -exactly- what you want but at least there's an option in some of the tight setups rather then not being able to do anything with those sides.