It is called a reaffirmation, and YES it can be done. Since your attorney knows about it he will be looking for it when you bring the paperwork in.
Your attorney will advise against it but bully him on this one and let him know you want to reaffirm this debt, Now, please keep in mind, if you default on this debt you will have no protection from any judgements or collections that can arise from the default.
The worst thing the Dr can do is tell you not to come back until you are caught up or demand payment BEFORE anymore treatment is given.
9 time out of 10 the trustee will do the reaffirmation since it is your sons best interest and his treatment plan.