Maybe you can put quotes around the fields, which should tell csv parsers that the commas inside are not field separators:

 sed 's/"/""/g; # escape existing " as ""
 s/[[:space:]]*,[[:space:]]*/","/; # replace the first , and the
 # whitespace around it with ","

 s/^[[:space:]]*/"/; # add a " at the start (and
 # get rid of whitespace there)

 s/[[:space:]]*$/"/; # same at the end'