I was thinking the same thing - use it both as an aux and for a tender. However, the long/short shaft requirement does rather make each suited for a different purpose. Also, for my Ribcraft I'll need an 8HP (using the 1HP per metre rule that seems popular) - and it needs to be quite a big tender to cope with that.
Therefore, I've decided that I'll get the aux for the rib, and some paddles when I get the tender, and face the fact that I will have to do some exercise. Having said that, rowing in to the shore has got to beat swimming in, which is always the other option!!