back to Cognitive Development Failure
Basically, it comes to transform the conclusion to playful situations.
Parents could take pictures of what the kid made and print them in the wall around his playing area he could consequently "refer" to it. after a while they could let him use the camera to take shoot and print them himself, eventually organize them over time, as in an evolution tree. The risk could be to stick with what he has done, to loop instead of going further. a curtain could help and parents could see how and when he wants to re-use his previous work.
You always need a different kind of new blocks to finish your self-invented structure. The kid could ask for x new blocks per period (ex : 5 new blocks per week). he would have to think about it and make the right decision. The other solution would be to let him design blocks since not all blocks exist. the risk is he could build solutions directly and break the brick model (making incompatible bricks).
Without giving solutions on how to do it, the kid could receive request when he is stuck. he would feel important and constantly challenged. He could eventually receive manuals but not the sequential manuals from the lego boxes. He could analyze what other people would have done as a reference work