There is another method you can try...
We had some nice wood that just was not the right dimension we needed for a full riser block. So.. it was sliced into layers approximately 1/8" thick, and glued together on the form, to create a riser. Of course, since it was "Form Fit", there was no light gaps once we did the glue up with laminations.
Started with these:
Glued back together in the form like this:
Comes out looking something like this:
Then shape the belly side.
Then you can glue it into a riser like this one.