No, but it would be easy to try out. Use a strip of craft paper as the between strip and tape the additional molding that you are going to use to the bottom, paint it, then tack it to the existing crown molding; or something like that.

We used this faux illusion in our former home. I wish I had pictures of it because I would love to do something similar in our new home. One of the great things about what was done is that we did not have to remove the original molding. They added a little something to the bottom--and then several inches below they added another piece. About 6 inches in from the edge of the ceiling they added another. The whole thing was then painted in a high gloss to give the illusion that it was all wood. It was fabulous!

yes, its 2 piece crown moulding.
I am a trim carpenter and we install 2 piece in alot of houses.
we normally use a piece of base cap run about 4.5"s below the crown.
once its painted one color it gives the illusion of a built up crown moulding.

it gives the look of having crown bedded on a piece of upside down baseboard. ( which is another 2 piece crown, with the true built -up look)

I have a couple photos of a similar method. Not exactly the same, but they might give you a visual. I like to use picture rail molding as the "other" molding beneath the crown. Picture rail molding allows you to use hooks to hang pictures/artwork off the rail molding instead of having to fasten hooks onto the wall. No nail holes in the walls with picture rail molding.

The "red wall" is a 3-piece, a backer of 1/2" MDF with standard crown up top and a piece of picture rail molding beneath it. I don't normally like the two moldings to be this close together, but it was what was wanted.

The "yellow wall" crown below is a larger crown, a 6-piece built-up, but with the same idea...the picture rail held a few inches blow the crown. This molding is about 11" tall.

In addition to using this to elongate the crown down the wall, you can use the same technique to pull the crown further out onto the ceiling, but it's style-dependent and only common in larger rooms with high ceilings.

Mongo,
This is great. I've been having a debate with my husband about this issue as he doesn't want nail holes and we installed crown molding that is 4 3/4" in two rooms with 8 ft ceilings. My husband is convinced that the picture molding needs to be hung lower on the wall because it is that way in his old apartment which has 10ft. ceilings.
I want it at the bottom of the crown so as not to break up the lines of the already small rooms.

I guess I am curious is you have an opinion on whether we would overwhelm the room now by adding the picture rail below the molding as in your preferred option above. Is there are rule of thumb for the space between the bottom of the crown and the top of the picture rail?

Of course I wish I had known his vehemence about nail holes before we put up the molding...

Any suggestions or thoughts most appreciated.