sounds like you might be talking about supercropping, but it doesn't give u more nodes. if u want tighter node spacing then lower light depending on type of light. if running floros i keep mine @ 3" & consistantly get 1" spacing. 600w mh air cooled i keep 18" above & get 1-2" node spacing. do this only in veg. go to resource page @ header of site do homework & happy growing!
If you want to bend stems down to accomplish LST, I think clothes pins can work. (I never thought of that, but may try it! )...You don't have to clamp the stem itself; many pins have a hole cut out to fit around a clothes-line, so I presume it'd fit around a MJ stem quite easily.
I've used bent paperclips with washers on one end, in the past.