Leslie - let me see if I have this right. You want to make the wax model itself hollow. So that the wax is lighter, you use less wax, there is less wax to melt out. You want the original wax to be hollow.
When I look at the photo of your wax...how big is this anyway?......
The only way I know to make a hollow wax form is by making a master parting mold of the object, basically making it possible for you to duplicate the form. You need to leave an access to pour the wax in, and small vents to let the air out. You can do this the same way that you might make molds for making waxes for metal casting, either by making a multi-part interlocking plaster mold that you would then soak, rubber band together, and fill with hot wax, then pouring out the still liquid warm wax, leaving a residue of wax inside the master mold, which would then be disassembled, and any flashing of the wax, or pitting of the surfaces being cleaned up with hot tools and polishing. AND THEN you could invest the hollow wax. Or you could make a one piece latex mold - using the original piece as the model - and then make a multi-piece plaster mother mold - to keep the latex stable and in place while you pour in the hot wax to coat the interior of the latex mold - then take the mother mold off, cut open the latex, pull out your original, put the latex back in the mother mold, fill and decant the hot wax, then disassemble the mold, pull out your hollow wax, clean it up, and then invest it for casting. The best reason for going through all these steps is to be able to make a series of the same objects, or to make sure you have a source for more wax models in case you have incomplete castings. It's a lot of work, and if that piece you have is as large as I think it is, you will end up with a monsterous undertaking involving lots of process materials, time, and physical labor. You could make the multi-part plaster mold, then coat the individual components with wax, and then assemble them, but it still means you need a wax -or clay, or wood, or whatever media - original piece to make a parting mold from.
You can make flat, thin sheets of wax by melting your wax and then pouring it into a wet plaster mold of a walled baking sheet, and then construct your piece using these thin sheets, tacking them together with a soldering iron, and building them leaving a hollow cavity inside (think of hollow chocolate easter bunnies - which is a good example of the use of parting molds and casting in series). Or you can take the same walled baking sheet, spray it with a good coat of water, and then pour wax to the thickness you want for your sheet, and pour your wax that way. I think the plaster mold is best, make sure it is soaked..meaning no bubbles venting from the submerged plaster.
After you get a hollow wax you will want to make sure that it is uniformly thick, and sealed. So you should check it by shining a flashlight inside to see if you can see the light from outside, and vice versa.
But I would be concerned about wall strength of hollow waxes, and also leaky joints where the wax meets up, because you don't want your investment leaking into the hollow cavity, or deforming your walls. That seems like a really big complicated piece that you are working on, and it seems you already have so many factors to control that maybe you don't want to make this any more complicated. Some one said to me 'it's easier to make the wax right than it is to try and fix the cast piece.' You Know?
You can check mold making processes for metal casting, or ceramics because slip casting is handled the same way. Think about it, find good pictures of the process, draw your ideas out, plan the whole process on paper, decide if it is worth all the extra work. This process is good for components that are repeated, and basic forms upon which you can make variations. They are generally a stock resource, not useful for a single shot. Good Luck, and a hug.