Which Airlines are you flying with? Some are better than others for this.

QF will make the bed for you in J, although a lot of people tend to do this themselves rather than wait or ask. BA on the other hand don't have mattresses in J, so the blanket trick works well.

QF F they are very proactive and will make sure you have the bed made properly while in EK F I have had them both be proactive and make it for me as soon as they see me move, but have also had them not offer at all.

Really does depend on the airline, and sometimes the day of the week and weather that day and what they had for lunch if you see what I mean