There is are two stages between "Doing a Study" and "Doing imaginative work" that you can use as tools to bridge the gap. It has been working for me pretty well so it may or may not help you!
The two "tools" you can use are:
- (1) Learn to draw it from memory!
- (2) Draw it from a different angle with plotted perspective
Sounds simple enough but let me clarify. Please note this is simply what I have found useful but things may be totally different for you.
1: To do this you must MUST simplify and work in stages, a bit like those "how to draw a [animal, face, mcguffin] in 5 steps. You can do this even my tracing the basic forms over what it is you are wanting and learn to draw each stage from memory building up. What this does is force you to actually learn and understand which bits are the important bits. If its a horse you want to be able to draw from imagination as an example you begin to learn which are the horsey bits that make it look like a horse and which are the bits the you can push and exaggerate. You are not really memorizing abstract lines but memorizing actual things. It forces you to understand your subject.
Also important for this is you copy ONCE, then hide your copy and ref and do from memory. Then unhide, correct, rince repeat. You do not just keep copying over and over as it doesn't work. Its the actual forcing you to remember that really solidfys it.
2. This vid talks about it a bit
http://www.youtube.com/watch?v=aDNhFLcsgh8. Basically you stop copying your ref but instead you "build it yourself". So plot a horizon and a couple of vanishing points and try to draw a really simplified version of you ref at what ever angle you have set up with your perspective lines. Again this forces you to stop understanding your ref in terms of its abstract 2d shapes but actually understand what it is in space. (almost the reverse of Betty Edwards stuff, which is also important at the beginning)
The things you are actually drawing here could be animals, bits of anatomy, cars, planes, buildings .. what ever you like that you think might be useful for when you start jumping to scenes from imagination.
Also important is because it is impossible for you to be just mindlessly copying it can reveal any fundamentals that still need work like perspective or form.
I hope this is helpful and good luck. Feel free to ask for any clarification or tell me I am totally wrong! :)!