The answer is unequivocally: No. Consenting sexual activity involving only a husband and wife cannot constitute "fornication" according to JWs.
Within a marriage, oral sex and anal sex are merely "uncleanness" (similar to the use of profanity or viewing of soft-core pornography). Officially, Jehovah's Witnesses eschew all uncleanness. Unofficially, a couple who occasionally dabble in the practices are expected to work on their own to overcome it. They can involve elders but they don't need to and it's not judicial.
Only eventually, such as if one spouse continues to force it upon the other, the harasser may be considered guilty of the serious sin of "gross uncleanness with greediness". Another hypothetical would be if either or both spouses seem to advocate the practices, then they may be considered guilty of the serious sin of "loose conduct" (that is, a brazen disregard for propriety). Neither form of serious sin allows divorce with the possibilty of remarriage, per JWs.
The fact that someone heard something from some elder somewhere is worse than useless information, since there's both hearsay and a good chance the original hick elder was wrong anyway. A recent letter to elders says that judicial committees continue to try to disfellowship people for soft-core pornography, even though in most cases it isn't considered a serious sin (the branch reverses disfellowshippings like that). Also, the Flock book clearly states that the victim of rape has not committed fornication; the fact that they have to spell out something so obvious is strong evidence that certain elders are so ignorant it's scary.