I have been looking for a way to both fill voids and also a way to use epoxy for embellishment. I just came across something called Milliput, an epoxy putty. It's a putty that comes in two parts. It will not flow into small,crevices unless forced but it might be a solution for large cracks.
I plan to use it for embellishment. Probably by cutting a grove and then filling it with Milliput.
I have used five minute epoxy to fill in a large void in a piece of oak burl. I used duct tape to build a wall and the poured it between them. It turned fine afterward.
Has anybody else here used Milliput?

If I had that piece or one similar... This is what I would do, first put down a thin layer of CA glue as a base coat, in the gap to be filled. Let that dry.  While it is drying mix your filler.  The filler I use is a filler that a friend of mine uses to fill in cracks or gaps on fiberglass airplanes.  It is baking powder (NOT Soda) with a several drops of food coloring to add color.  (Sample recipe: Turquoise filler: 1/4 cup baking powder, 15 drops blue, 5 drops green in a plastic bag. Squeeze the bag and contents until well mixed.)  Apply a thin layer of filler over the dried CA glue and drop thin CA glue over the top. (Remember the CA glue has warning to not breath in the odor from the glue, so use caution)  Continue to layer until the gaps are filled. (don't get in a hurry let each layer dry and don't use too much filler at one time or you may wind up with dry spots in your filler.  Rotate the piece as you fill in the gaps so the filler doesn't fall out as you work.  Let the glue soak through and harden with each layer. Slightly over fill the gaps, (so that the filler can be turned or sanded smooth to the level of the wood).  Once it is completely filled let it set overnight.  It should be ready to turn by the next morning.  I will usually power sand the area filled so as not to chip the filler out as I turn it.  I've made some really stunning pieces using this method as well as saved some beautiful wood. 

Should you prefer a different color, here are recipes:
1/4 cup baking powder with one of the following for color ( I use McCormick food coloring)
Orange 6 drops red, 14 drops yellow
Chartreuse 24 drops yellow, 2 drops green
Peach 3 drops red, 9 drops yellow
Purple 10 drops red, 4 drops blue
Turquoise 15 drops blue, 5 drops green
Rose 15 drops red, 5 drops blue

Once I have mixed my filler, I usually put it in a bottle with a small opening so I can direct the flow of the filler.  As long as the filler is kept in a dry place it will last and can be used for other projects as well.

Note: The color as mixed in the powder may be lighter than expected. Once the glue is applied the color will darken.  Colors are limitless using this method, so mix your own, varying the drops of color.   To test the color, take a small amount out, put it in a small bowl or other container and drop a few drops of water on it.  This will show you the true color before you use it as a filler.

Hope this helps...