Kmay, my general advice for ANY snake that seems to be constipated is to soak in luke warm water.
My own Dumeril doesn't seem to have a problem with constipation, but my young Ball Python pretty much seems to like getting soaked so well that he won't go until I soak him. Oddly enough the same little guy doesn't seem to like the whole soaking deal unless I hold onto him... and the whole reason that I mention this here is the fact that if you are holding onto a snake while soaking it with the intent of getting it to defecate, it will be gross; just remember, it all washes off!!
I have a "small" (19qt) plastic tote (with tall sides and a locking lid) that I use alternatingly as a feeding bin or a bathtub for my young snakes. To soak, I fill the tote about 1 or 2 inches deep with luke warm water (so it feels slightly cool to you - and doesn't burn your snake). I do this for about 20 minutes at a time. If in that amount of time, no success; repeat the next day, etc.
WHEN TO CALL THE VET: Gently feel your snake as you handle him, and feel for any bulges near the vent. If it feels like there is a rock (which would be hard, dry feces/urates that would be very difficult to pass) just before the vent, then you would want to call and talk to a vet. If you feel a bulge but it is not significantly hard, keep trying the soaking thing for at least another week or so.
As far as feeding, if you are in touch with the breeder, consult them for their opinions on this. I am under the impression that Dumeril's Boas' metabolisms are so slow that the feeding regimen you are describing could be too much too often. I can't claim to be the expert there.
I hope this helps!
~Rebecca
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1.1 Ball Pythons (1.0 '05 Ghost, 0.1 '03 Normal)
0.1 Dumeril's Boa
0.2 American Pit Bull Terriers (40 lb darling lap dogs)