You are quite correct that the Clerk puts the meeting agenda together but it is an integral part of a councillor's role to bring issues to the meeting that have been raised with you (assuming, of course, you see merit in having the matter discussed).
Having said that, the specific item to which you refer may be fraught with danger. It appears from what you say that the matter might relate to specific councillors' interests in specific items. If so, the matter is not one that can be discussed at council. It is very much up to the individual member to declare his/her interest in a matter, it is not for the council as a whole to debate it. Even if a situation arose where a member does not declare an interest but other members feel he should, the council does not have authority as such to compel a member to declare.
If, however, I have mis-interpreted your post, and all you propose is a disussion on interests in general, this could happen for essentially this might provide an opportunity for your clerk to advise. This would not I think, justify excluding the public.
I would be interested to hear Counterpoint's veiw on this.