John - I have tube fed small Eggeaters (marcbt - and larger ones )before and would push the tube about 1/3 of the way down the body. The tubes are smooth with the rounded tip so there is no reason why the snake should be hurt during the process. Just be sure to inject very slowly. With egg, the hole in the tube tends to feel like its blocked and its natural to want to push harder, just be very careful when this happens.
As I mentioned above, try get in touch with the finch breeders and do what I did.
Try Pat De Villiers in Camperdown, he has loads of finches.