I would dose him with Flagyl(Metronidazole) at a dose of 50mg./per kg. body weight. Then a second dose of the same 10 days later or so. DO NOT attempt to feed him at ALL during this time, and wait approx. a week or so AFTER the second dose to feed him. Make sure the meal is very small too for a couple feedings to see that all goes well and greatly lessen the chance of another regurgitation. After he has kept down a couple small meals, you can gradually step-up the meal size back to normal-sized prey.
This is a very reptile safe antibiotic, but it kills both bad AND good bacteria which is needed for proper digestion along with fairly warm temps(low 80's). You can also administer a bit of "pro-biotic" such as "Nutri-Bac" to help things out as well. This is good bacteria that helps replenish what was initially lost in the snake's gut. Kathy Love also sells this at shows on her table quite often.
http://www.reptileuv.com/nutribac-df-probiotic-for-reptiles.php
Flagyl can be found in several oral forms, pill, paste, and liquid. You can get this from any vet, or order some online at a number of places too. Some farm stock stores might also carry it too. Approx. 1/16th of a well-crushed 250 mg. pill doses a 300 gram snake. Add about .05(1/2 cc)of water in a small shot glass, and mix as thoroughly as possible. It doesn't ever totally dissolve, but just mix well before drawing it up in a small syringe with a thin tube attached, hold the snake upright, and ease it down the throat several inches, then slowly press the plunger as to let gravity help it flow into the stomach and not shot back out of the mouth. It is very simple to do actually. But if you don't feel comfortable doing this for whatever reason, go get it done by a vet for a few bucks. you don't want your snake paying the price for not getting it done one way or the other.
I have seen a great number of snakes die from people not doing this in time, so I would STRONGLY suggest you do this ASAP so this doesn't happen to yours too. I have used Flagyl after regurges in the past with absolutely FANTASTIC results, but follow the above steps to the letter, and things will work out fine.
Hope the snake gets back on track soon!
~Doug
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"a snake in the grass is a GOOD thing" 
my website -serpentinespecialties.webs.com