I have a share in an Auster which i have often had to start by swinging it myself with no one in the cockpit. I set the throttle with the friction nut very tight, tie back the stick with the harness, set the park brake and always use chocks. I used to tie down the tail when possible, and will probably resume doing so - as well as switching the fuel off. I think it is safe enough provided you always take it very seriously and double-check everything which I always do. I've heard some swing the prop from behind so you can reach into the cockpit through the window if needed - have never fancied trying it though!