Yosef Karo

“ However, if he says [to the baker] , "make an eruv for me," he acquires possession of the eruv. Even if he says "Transfer possession of an eruv to me," if he gives him an object according to the rules of possession in order to buy a part of the eruv through the object, he acquires the eruv. Similarly, if the baker transfers possession through someone else or buys bread from the market using the money given to him, [the first person] acquires the eruv. If one gives money to a layman and tells him "Include me in the eruv," he has acquired the eruv. ”