Currently the only thing preventing easy creation of these blocks is the protected variable that loads minecrafts default texture file.  The render for falling sand uses the proper sprite index but you need to add your own entity and render all just to get it to use a custom texture file and I have spent probably way too much time than its worth trying to get that to work with no avail.  Adding a hook in the RenderFallingSand to be able to change the texture would be huge!!! Thanks.

There isn't much need for this if you can make your own entity for it. Is it more work? Yes. But having a hook to change the texture seems pointless to me if you can just make a clone of it. (plus then you can customize it, have it spawn particles or somesuch, or speed it up, give it properties. If you don't want any of that then just clone it.)

I'm not an expert coder but I spent hours on this and I still haven't been able to get the custom sand to act like the regular sand even when I've copied it exactly and just changed the texture.  The sand would disappear during most of the fall.  I know the custom render was working because of tweaks to the file would change some variances of it, but the exact same code.  Why the need to add a custom render and entity all to accomplish a custom falling block.  Especially when you've looked around for help on the issue and EVERYONE seems to have a problem accomplishing this.  It would be the slightest bit of change to the code would go miles.

I'm pretty sure that this will be done by Minecraft in 1.5, support for ids over 128 was added in a snapshot.  So no hook is needed. 

While this would be a simple edit, it is unnecessary due to the texture changes in 1.5. Forge texture system won't even exist.