Yekke, your last post is obviously the basic answer, especially since we can say that in Chutz La’aretz he didn’t do Kedushin, as the Ramban writes regarding all other Mitzvos.
Also, even if we find that the Avos kept the Mitzvos, it’s not like they were Bar Chiyuva. It was more like an Inyan. In more Halachic terms, their Kedushin probably had the status Kedushei Ketana and Maamar.
The other answers are more like Afilu Im Tirtze Lomar…