I don't think you can do that, the ship leaves Funchal in the morning and returns in the vening, so the only way is the opposite to what you want. (I think)

My wife and I did the daily trip back in August from Funchal to Porto Santo and back again. We bought tickets from registered office in Funchal while there and not before hand. We were able to ask the questions we wanted to hear about and paid for the transfer from hotel to quay and back again later that day. It was a long day as had to be up at 5am and got back into bed after midnight so keep that in mind.

We upgraded to 1st class/premium lounge which gave us food on each voyage. We could have taken a pack up to eat on boat but did not want to try and keep food chilled during the day on the beach. Your benefit will the choice of dining in Funchal before your return sail. The lounge has a tv and private bar and nice seats and private viewing platforms to the front of the boat. We did not think it was too expensive especially as it was desired trip we wanted to make.

Boat has movie theatre so you can watch a film on both crossings. On our trip it was a different film on each crossing.