I'm pretty sure that they do this for a good reason so want to keep it this way.
Yea. When you save a serialized object in a database, your queries won't be able to perform any tests on the object; e.g. test whether one date is later than another one. In addition, you are making your application vulnerable to the problem of incompatible serial versions. (That's probably not an issue in this specific example, but the issue comes up repeatedly in SO questions ...)
My question: is there another way? I would like to get rid of the additional date field.
Unfortunately, I don't think there is.