DGAC L'arrete du 17 juillet 1992 precise que: "l'integration sur un terrain non controle s'effectue au debut de la vent arriere, a la hauteur du circuit d'aerodrome en assurant une separation visuelle avec les autres aeronefs deja engages dans la circulation d'aerodrome et en leur laissant la priorite de passage"
The same arrete indicates in a paragraph that joining should not be effected without prior reconnaissance of the aerodrome, but that this reconnaissance should not be obtained by a passage a' la verticale unless this is a practice that is often used at that aerodrome.
So I may have over egged the chances of being jailed for doing an OHJ, but it sure is not considered a safe procedure.