I did a quick search in 'feature requests' and discovered coupon codes for members wasn't an option right now and had a passing thought...
Someone correct me if I'm wrong but there's nothing stopping me from pricing a group membership or course at a lower rate during a group or course launch then changing the price a week later.
Also, maybe organising a date and time with selected members where by changing the price of your group or course for 10 minutes or until those selected members have successfully subscribed or purchased the course at the discounted rate. Would there be any complications doing this?