he started jumping in at every lul in the evening and was doing up to NINE songs in an evening

Perhaps if this starts happening the "jump in when ready" approach needs to be tempered by a bit of firm-but-fair MCing. JIWR is brilliant when it works - I love the flow of song from one voice to the next - but I don't think "have you got one for us, Silas?" disrupts the flow or harshes the buzz excessively. Or "have you got another one for us, Pip?" That works very well, I find.