How to include an ecnomic game where participants are "paired" with a fake person I created?

I want to include an ultimatum game on my survey. I know SMARTRIQS allows for this, but from what I read, it would pair real participants together. I want to make participants believe they are being paired with someone in real time, but in reality, I want them all to see the same target (i.e., a picture of this target preson and a brief bio about her like you see on dating apps). I would also like them to be able to upload a picture and short bio themselves if they choose to, just to keep up with appearances, but this is not necessary. My main interest is giving the appearance that they are being matched with someone, such as having a loading wheel on screen as they are being "paired" followed by the profile/bio of this target, and then the option for them to upload a pic and/or bio in return before proceeding to questions judging the target (e.g., how likeable does she seem) and then have them do the ultimatum game where the participant is always the receiver who can accept or reject the target's fixed offer. Any ideas on how I could set this?