Thank you for your help.Meanwhile, I found on the FamilyTreeDNA website the following statement:
"Select the right person to test. Do you have the same y-Chromosome or mitochondrial DNA as the ancestor who interests you? If not then you will have to find a relative to act as a proxy."Therefore, it seems that it might be common to use a proxy, such as my brother.
(Now I am awaiting an early summer sale, which hopefully will come soon!)