Sources close to Ryan Deluca -- who founded bodybuilding.com and runs a VR company, Black Box -- tell TMZ he and his bride-to-be, Nelya, learned a whole 1st dance routine to Montell's hit, "This Is How We Do It." But Ryan wanted to go the extra mile, and get Montell live.

We're told one of Ryan's groomsmen was Creston Thornton, a Live Nation bigwig ... and he called music agent Jamie Adler ... who scored Montell for the Boise ceremony. As they say, it's all about who ya know.

Still, getting Montell to Idaho wasn't easy. We're told he flew private from Rome to Vegas (where he also performed that day), and finally to Boise. Ryan covered travel costs and the $10k appearance fee.

MJ performed 3 songs and, most importantly for Ryan ... Nelya loved the surprise.