I reckon it's possible to argue that there is an offside line at the tackle (even though the lawbook states otherwise), regardless of whether there is a ruck/maul formed.
If there is a gate, there are entry points and therefore there are offside lines. We don't allow players (other than the tackler) to come through from the opposition side of the tackle, the lawbook calls it "incorrect entry" but it's just another form of offside - specific to the tackle situation.
There are a number of penalties that could be brought about at the tackle- legal tackle, release tackled player, assist tackle, separation, rolling away, entry, loitering, playing a player without the ball. The referee just needs to go back through their checklists.
I recall a practical example of the definition of a ruck from my days as a Development Officer and the example was two people (one from either team) standing/crouching over the ball on the ground shaking hands - it fits all the definitions for a ruck. Maybe we need to interpret the lawbook like this?
I think these types of tactics/interpretations are a blight on the game, Rugby has enough issues as it is without muddying the waters any more!!