In Egypt, may G-d preserve it, when a festival occurs on the Sabbath eve, the custom of the sages in all synagogue communities is to perform eiruv tavshilin for the entire congregation, because there are many congregation members who are not knowledgeable in the performing of the eiruv commandment, and an announcement is made before the congregation to the effect that anyone who did not prepare an eiruv may depend on the sage's having done so.
I was once asked by a certain sage who had forgotten to properly perform the eiruv by including others as it should be done. In my modest opinion, it seems one may be lenient on the issue. I can almost say that since he is accustomed to always perform the eiruv and including the congregation, that there is no need for another to do so… the Halacha tends to leniency in eiruv, and we would say that since he is accustomed in doing his eiruv with the intent to exempt the others, one may consider that his eiruv was fulfilled for him by others, as it were… for by virtue of this fulfillment - that fulfills for others who depend on his eiruv - there is no loss; one profits and the other loses naught, since the eiruv, in any case, benefits the others yet not at the expense of the one performing it. We therefore find it fitting to consider that it is as though he were exempted by others.