Selling carousel unit for interest?

Is it possible to sell your carousel unit for interest? For example, say you have 8 gold going into stage 3-3 carousel and you pick up a 2 cost unit during carousel. Can you sell that unit before 3-4 to gain interest? I don't seem to have that option, as my interest generates instantly after carousel round. But I was watching a stream and there was a stall in the streamer's interest generation that lasted long enough for him to sell his carousel unit and gain 1 more interest for stage 3-4. Is this intended?