Kodoku, i hope the following page deals with this ko's, or next time remember to kill them all. It only brings bad memories of the "selfish mother" story =< which many of us still have scars because of it's abuse of karma houdini.
First, some yukkuris survive. This is unforgivable. Grade A methods ensure that all yukkuris are eliminated.
Second, if the kos defecated inside of their mother the feces would diffuse they would have to endure the bad taste in order to eat their way out. Although some yukkuris have been showing tolerating pain and nastiness to survive, it is unlikely that these children of deibu would.
To clarify, these types of kos have been shown to be simply demand care and goods from their mother without making any proactive attempt to save themselves.
One can easily combine methods and, say, smash the koDeibus with a book, tape their mouths shut with tape and pump them with air until they explode, subject them to a raper, or splash them with sweets and watch them feast on eachother - but this is just the illustration of a singular method, not a compound one.
The actual taste of the expired bean paste appears to only be repulsive to Yukkuri if they realize what it is. As is often shown (including method 7, where a Deibu enjoys poop thinking it's real food), they can often mistake it as food, so munching through the walls of the mother's mouth shouldn't pose an issue just because of the diffusion of poop.