Ok here is my idea but I would only suggest that you do it if you had a friend that can weld and can trust his welds. Payment can be worked out like lets say a case of beer or an I Owe You.
Now the key here would be proper welds, bracing and guessets. The more strength the better. I am using Rattlecan's pictures of his build for reference. Now forgive me on my photoshop with the 3rd picture I was in a hurry.
This would work if you didn't mind on welding to your frame. You would have to calculate the difference between the front of the leaf spring and the rear of the leaf spring. To have the leaf springs sit right, this way you could retain stock leaf spring but still get some height. As for the rear you could spend that money you saved on the front and use it for the rear. Now this would be my idea, I have many friends that are certified welders and would be happy to weld this up for a case of beer and I have access to my school shop that has tons of scrap metal with different size's and thickness if this happened to be my situation. Now in your case you might not have any friends that are certi. welders or have and access to peice's of scrap metal but its just an idea.
The only thing that would consern me would be the two metal flat straps that are bolts to the frame and leaft sping. Those two straps would have to be definitly re-enforced. That would be your one weak link. Again this could be a bad idea but it was just an idea and also safety is the key thing here as stated above sometimes it better to be safe and save up for the proper stuff than to chance it.