I remember years ago, while playing cards with friends in Germany, my bemused realisation that I had been using the German equivalent of 'if only I had known that' effortlessly for some time, simply because I heard it in context. I could never produce it when I had to think about it logically and grammatically in my German class at school; juggling with word order and subjunctives made that impossible.
Drilling comes in and out of fashion. There are grave dangers in drilling that involves context-free, mindless repetition, but it can be used profitably with his type of structure, in my opinion.It is not trivial. I wish I had more solid help I could offer in this important area.I'm sure a lot of you will think this is so trivial a topic compared to the loads of work done in this area. But, this is just an idea I'd like to have more information about.
For those who have not read it, there are some very interesting suggestions in this book:
'Implementing the Lexical Approach' by Michael Lewis