So lets say you have a synth vst, and it has no LFO, but you want to assign an LFO to the filter cutoff or some other parameter in the synth. At the moment, I know you can modulate whatever synth parameter you want by drawing it in with automation, but is there any software LFO that you can assign to a software knob?
good question!
i’m not sure about it…
What about throwing an Ableton Frequency Shifter plugin onto the track?
Then from there you could play with the LFO and automate that…
Dunno if that will give you what you want. But it might…
I think an all purpose LFO is coming in the next version.
IIRC there are many threads about this over on the Ableton forums. There is LFO Everything for M4L too if you have that.
If you have max for live like me someone has made an LFO Device 
yup. M4L has what you need!