one of the best mcs of singaounds I have come across is Chris Wilson
,   the secret is to know your singers or know some of them,so if someone sings something slow and long the mc can turn to someone with a bit of cop on,who he/she knows will not do a slowlong song ,the secret is variety.
singers please cop on its not about self indulgence,if two people have done slowlong songs ,please do something up tempo or humourous