well, nepenthes clump in tc I have heard (it's the whole way they are produced, leave one plant in culture, and you get hundreds)
Clumping is something I think you just have to wait on...
ways you could possibly speed it up are layering the plant, essentially bending it down to the soil, and covering a dormant node with soil, and repeat as neccessary, never taking clipings...
cliping also forces dormant nodes to activate, this could COULD start a clumping effect, but I think it would take a long time, I think Cindy, or maybe someone else was experimenting with this...
and finally, you could use kiko paste (I think that is the right name) that inhibits the flow of a hormone, and causes the plant to start branching out.