The fact that none of these things happen in all concerts shows that they can all be done away with.
--- the sponsors get their name in the newspaper and sometimes in the programme details at the hall. They very often, especially if they happen to be finance companies, have a banner, sometimes even on-stage. They only attend a very few of the events that they sponsor, and it is not often that I have seen them given any momento. They probably do not want such a thing anyway; why would they want their money, which they have given philanthropically for the love of music, and economically for a little advertising, spent on themselves. No need for speeches on account of sponsors.
--- no need to garland artists, or to buy them shawls.
Why not just increase their pay? they cannot eat shawls, and cannot even wear them in this climate; garlands are a complete waste of money, protocol demanding that they must modestly remove them straight away.
There is plenty of opportunity for this kind of ceremony in those events which are functions with music attached, celebrations, releases, honouring of individuals, presentations and so on, and there are plenty of those to go around, so those who want speeches, shawls and garlands need not feel cheated.
---but if we must... have a very few words of thanks to artists (and there are concerts I've been to where I have never found out who one or more accompanist was!) and mention of sponsor, then, as Arasi and Shankar say, before Mangalam is the best, and perhaps only suitable, place for them.
I don't even mind an introduction, so long as it is just that; a welcome and an announcement of names --- but no biographies, please (preceded by the obligatory words, "abc needs no introduction...") and no speeches.