I've had this picture in my inspiration album for a minute and have wanted to do something similar, unfortunately my monkstraps lack the substantial heel and moc toe that I feel makes this looks so interesting.
Saw your post with that pic late last night and stuff kinda clicked. I've had an old thrifted pair of size 40 tux pants waiting for a rebuild. I knew I was going to take them in at the seat to help get the size down, but needed to take the same amount out of the front to keep pocket placement from getting weird. I ended up redoing the front pleats, then sewing the front together from the pleat all the way down the front seam. Worked out really well, in addition to some tapering on both sides. Still haven't re-pressed anything or trimmed all the excess material from the insides, so they'll bunch & stack a little less eventually, but honestly I like it given how skinny things got.
Sorry for the pic quality, everything's been pretty quick & dirty
Warning: Spoiler! (Click to show)