Missed I have a possibility to modulate the speed of the LFO. Why not to a modulation envelope implement? Put it in instrument editor envelopes you can. For on/off control you could use checkboxes. Or for more control value boxes which could control the amount of modulation, so same could be applied for many LFOs with different amount.
¿huh?
e:I mean the instrument LFOs. But you probably already got that?