I don’t know, and I couldn’t find any information online on this question.
I would guess that if no other table can be found, and it were to be used for the purpose of prayer, and nothing profane, God would desire it to be used as such. However, it should only be a last resort, and only used in this matter for the purpose of prayer. The reason for this is because the credence table is a part of the “physical structure” of the mass, and part of the sacredness of the mass is recognizing that we need to keep it “separate” or “set apart” from the rest of our daily life. However, if its going to be used for prayer, and no other options are available, the credence table is still fulfilling its purpose as facilitating the relationship between God and man through prayer. But perhaps Fr. Angel, at Fatherangel.tumblr.com would be a better source of answers for you. Hope this helps!