You tell them its none of their business why you're not auxilliary pioneering, and besides a reasonable argument can be made as brought out in this thread that pioneering isn't even Scriptural. Then again, that might not be such a diplomatic way to handle that. Might be better to say that your circumstances just won't allow it at this time, and that you're planning on at least increasing your time this month.
After the letter was read at my congregation, a good hearted Regular Pioneer approached me and asked me whether or not I was going to do it. I posted that account somewhere on here, I can't recall what thread. I told her at the time that I didn't know, which was honest because I really didn't know at the time. She grabbed my hands and arms and shook me and got right in my face. It was really awkward to say the least. I kept my cool, and told her I'd let her know. She actually gave me a time table on when I need to let her know. She offered to assist me in getting the time in a Lucky Luciano kind of way if you catch my drift. Couple weeks later she apologized, which she didn't have to. I know she meant well, and I love both her and her husband. Good people in my opinion, and I enjoy their company. They're ok, just misled, but if it makes them happy, then thats a good thing.