Classic problem. We all have been there. What have you actually tried to make the dream longer? You say "all sorts of things", but can you be specific.

One thing I notice is you talk about trying to control the dream. That should never be your first goal. Attempting to dive right into what you imagine LDs should be is going to shorten them. Your first step should be to pull more awareness into it and get the sensory experiences stable and intensified.

Let me know what you have been trying already and I will respond more after that.