Create a FIFO or socket or shared memory segment in the effect, make it available as a read-only parameter, send the handle of it from your plugin to the editor/s. (Use non-blocking send, and perhaps also let the GUI send occasional “I’m here” messages so the effect can stop trying to send when the GUI isn’t open.)
Still only works on a single machine, but (depending on which specific API you use) may work cross-processes. It’s also better than just jamming data into a single global buffer, as it still nicely separates multiple instances, and would theoretically let a crash on the GUI end not take down the processing end (again, if the host was appropriately multi-process separated.)