Originally Posted by kiwidude
@Man Eating Duck - the code Kovid has written is dependent on having the data structure used by the conversion pipeline that Modify ePub intentionally avoids using. Which means I have to rewrite what he has done basically. Given that it is listed as "experimental" currently if it ever happens then it is only going to be after it has been in calibre for a while longer as I don't want to have to continually be changing my version of it.
I do have a solution to the problem...
You convert the original ePub > ePub with font subsetting on. Then you extract the fonts from the converted ePub, put them back into the original ePub, delete the converted ePub, rename the original ePub and edit the database to remove the reference to the original ePub. I know it can be a hassle to do, but it should work.