Just wanted to add my datapoint. Called 833-727-0118 and received an agent in their Philippines call center. Asked to place a hold for an award booking while my points were in transit from my credit card. Received the standard response that award holds are not possible.

However, I pressed further on the issue, stating that I and colleagues of mine have been able to do this recently, and so I know that it was still possible. I also told her that I had just made a J booking earlier today for my outbound and wanted to secure my return while PE seats were still available. I don't know if that recent booking swayed things in my favor, but after putting me on hold to speak to a supervisor, she came back and told me that they would allow the hold as a one-time exception (she repeated the one-time nature several times).

Looking back, what I should have done while I had the points in my account for the outbound was to go through with the award booking for my return flight until the final step. That creates the hold. Once that was done first, I could've proceeded to complete my outbound J booking.

My points were coming from different sources. I transferred MR for my J booking, which was instant, but am using UR for my return in PE. Status for the hold is shown as "Reserved." Agent told me that I would be able to finalize the booking online once the points are in my account, but I could also call back in if I'm unable to do it through the site.

Edit: Points showed up two days later, but was unable to complete the booking online. Had to call back in and the agent had to make a manual change to the booking to "unlock" it so that I could complete the process online.