Years ago I did this for an adult friend. I thought my friend would enjoy shopping and getting whatever she wanted. So at HS, we were approached by a Gifts of Lifetime person who told my friend they were looking for people to do secret shopping and she was to purchase whatever she wanted with ...can't remember, but I think it was $100 in Disney Dollars. and then report back on her purchases and why she selected those things. Of course she jumped at the change to "participate in the survey" . We had fun shopping and then met back up with the lady. Talked about purchases for a few minutes and then she presented her with a big wrapped surprise ball, which took her awhile to unwrap and inside the ball was a glass swan and a note. (the swan had meaning to us) and that is when she realized I had set the whole thing up. While she was unwrapping the ball/gift, the GOLT person was taking photos.
Yes, it cost quit a bit, but it was fun to do once. And, the company is legit and dependable. I helped create the event myself, but they will provide ideas for you too.
The only draw back is that it does (or can) eat up a lot of park time.