Move light closer or increase intensity, that will stop them running.
Have oscillating fan running, that will make stemps stronger.
Add 2 cm hill around stem or do something like in this week photos
growdiaries.com/diaries/168958-grow-journal-by-asnoriu/week/948249
Its way too early for LST. Would say you need good 10 days till then. Fat soft gardening wires works best. Buy and prepare.
Have a look at most of my diaries or this week :
growdiaries.com/diaries/184731-grow-journal-by-asnoriu/week/1046986
Read about lst, have in mind - all training should be done before watering, while plant is lanky, not crunchy as would be after watering, this will prevent splits and breakage.
Have fun !