至於

至 = 一 + 厶 + 土 : Mnemonic symbol: one of these conveyor belts from which you pick up your suitcase when you arrived at an airport. James II of England (zh) finally got the package he was waiting for! He picks it up from the arrivals (至) in the bathroom of the space station (Ø4). In it is a flute (一), which he sticks into his nose (厶). He blows his nose, and boy, does a lot of clay (土) come out! He's glad to have a free nose again.

于 = 亅 + 二 : Mnemonic symbol: prepositions are what glue the sentence together. Honey is as sticky as glue, so I'll represent 于 by a honey jar.

Yu the Great was assigned to repair the electrics of the space station's entrance, but instead she was snacking some honey from a honey jar. Now her capacitor got stuck in the honey and she has to use a crowbar to lever it out.