Rummikub buying two jokers
From these rules:


  A joker that has been replaced must be used in the player's same turn with 2 or more tiles from his rack to make a new set. 


So if you have retrieved a joker from another set, you must place it with tiles from your rack (this can also be a joker). Which could be interpreted as place the retrieved joker in a set using only tiles from your hand.

I know it does not explicitly says you can not use tiles from the table, but the "with 2 or more tiles from his rack to make a new set" is clear enough for me. 

Of course, you can always add house rules. Or the rummikub set/edition you have may have different rules.