Try bypassing the hunt group altogether with a daisy chain, by setting 221 to call forward to 222 on 4 rings and busy, 222 to CF to 223, and 223 to the voicemail after 6 rings but not on busy, so that 223's VM will not pick up all the calls. You won't have to mess with hunt groups at all.
And if you really want to do line redirection, keep in mind that this will tie up 2 lines: the first where the original calls came in, the second line where the call will leave again - for the duration of the conversation. If they're strapped for lines, this means that the next couple of calls could get a busy.
Have your tried Feature 4 call forward instead? You need to enable Line Redirection on the phone set, and then it will allow off-premise forward (at least for MICS4.1 and up) for the extension without tying up two lines.
Or to bypass the phone system completely, have them put on Call Forward on the lines from the CO.