I was wondering which Church document deals with this.
I suppose all one can do is to politely explain why you could not commune afterward. I cannot address “going up” for some blessing, but would recommend it be avoided since it may confuse your intentions.
Perhaps some sources will aid you in this explanation. You may benefit from reading more than these snippets below, however.
As the Directory for the Application of Principles and Norms of Ecumenism [1993], #129 notes, “Eucharistic communion is inseparably linked to full ecclesial communion and its visible expression.” You may review the document at
vatican.va/roman_curia/pontifical_councils/chrstuni/documents/rc_pc_chrstuni_doc_25031993_principles-and-norms-on-ecumenism_en.html
In limited conditions, the reception of Eucharist, penance, and anointing of the sick from certain non Catholic minister is permitted, but only under those conditions given in Canon 844 §2. A chief condition is the validity of the sacrament. However, the ecclesial communities of the Anglican, Episcopalian, Presbyterian, Methodist, Baptist, etc. traditions are not considered to possess valid Holy Orders or valid Eucharist. Thus it is not possible for Catholics to receive communion in their services.
“The Catholic faithful, therefore, while respecting the religious convictions of these separated brethren, must refrain from receiving the communion distributed in their celebrations, so as not to condone an ambiguity about the nature of the Eucharist and, consequently, to fail in their duty to bear clear witness to the truth.” (John Paul II, encyclical On the Eucharist [Ecclesia de Eucharistia], no. 30.; available at
www.vatican.va)
Also see appendix II, “May Catholics Receive Holy Communion In Other Christian Churches and Ecclesial Communities?” at
nccbuscc.org/dpp/Eucharist.pdf .