Thanks for your comment, it's prompted me to update in case anyone's still watching...
I last posted in April, when he started eating and passed the blockage. Over the next 2 months he continued to take very small meals, and no more lumps formed. However, my male snakes bruminate for about 4 months over the southern hemisphere winter, between June and October, so he went off feed again with the others. During their winter "fast" I offer food about once a month, but I don't push it if they reject it.
I figured it was best to just let him do what comes naturally, and that not eating at all would give time for any healing to take place before I tried any larger food animals. It's now warning up again, so 5 days ago I offered food and he ate VERY eagerly, a week-old chick and a small chicken wing.
So, he's definitely back on the food train, now I'm just waiting with baited breath for confirmation that his system is working properly - checking for poo on almost an hourly basis at present!
