Hi,
first of all the basis for appeal:
Article 106107, 108
Decisions subject to appeal
(1) An appeal shall lie from decisions of the Receiving Section, Examining Divisions, Opposition Divisions and the Legal Division. It shall have suspensive effect.
(2) A decision which does not terminate proceedings as regards one of the parties can only be appealed together with the final decision, unless the decision allows a separate appeal.
(3) The right to file an appeal against decisions relating to the apportionment or fixing of costs in opposition proceedings may be restricted in the Implementing Regulations.
This seems to be the case here, then
Rule 99
Content of the notice of appeal and the statement of grounds
(1) The notice of appeal shall contain:
(a) the name and the address of the appellant as provided in Rule 41, paragraph 2(c);
(b) an indication of the decision impugned; and
(c) a request defining the subject of the appeal.
(2) In the statement of grounds of appeal the appellant shall indicate the reasons for setting aside the decision impugned, or the extent to which it is to be amended, and the facts and evidence on which the appeal is based.
(3) Part III of the Implementing Regulations shall apply mutatis mutandis to the notice of appeal, the statement of grounds and the documents filed in appeal proceedings.
Next
Rule 100
Examination of appeals
(1) Unless otherwise provided, the provisions relating to proceedings before the department which has taken the decision impugned shall apply to appeal proceedings.
(2) In the examination of the appeal, the Board of Appeal shall invite the parties, as often as necessary, to file observations, within a period to be specified, on communications issued by itself or observations submitted by another party.
(3) If the applicant fails to reply in due time to an invitation under paragraph 2, the European patent application shall be deemed to be withdrawn, unless the decision impugned was taken by the Legal Division.
In fact you can form your claims in a similar way as during the examination procedure in form of main and auxiliary requests (but please respect the sensitivity in view of adding new matter and also the time-lines of the appeal procedure).
Best regards
Patmatt