I would actually suggest altering the behavior of these blocks so that they mimic they have directionality. The "glass" side always places facing you; however, the block also has a "adhering" side that always faces the block upon which it's placed. The One-Way Glass block will then mimic the appearance of the block upon which it's placed on the side opposite from you.
Some caveats with this behavior:
1- If you place a One-Way Glass block on top of another One-Way Glass block, it will attempt to mimic the appearance of whatever that block is mimicking. So, if you place a One-Way Glass block on top of Oak Planks, then another One-Way Glass block on top of that, they both have the appearance of Oak Planks.
2- One-Way Glass blocks can mimic transparent blocks; however, obviously someone one the other side can see through it as well. For example, if you mimic Ice, someone on the other side can see through as they can see through a normal Ice block, but you'll see through as though you're looking through Glass.
3- One-Way Glass does not mimic the opacity of the block it's mimicking. This is partially to avoid any weird coding issues, but also to give players the opportunity to identify One-Way Glass if they pay close attention to any lighting anomalies.