I have read of a dodge that I have not tried: buy an extra-long spoke for this job. On the spot put a 90 degree-plus bend in it where you would need it to be, then just 2mm later, where the head would be (the width of needlenose pliers tips?) put another 90 to direct it back to straight. Threading this into place can be done without removing the freewheel and apparently it does the job.

I'd be interested in hearing if anyone has actually done this...