Howdy Chris,
This is possible with a two step process per event. Depending on your desired outcome an optional third step might be necessary.
1) Create the event ticket with a set stock count.
2) Purchase the tickets yourself. If you set the stock count to one and purchase one ticket, the sold out notice will display. Likewise if you set it to 100 and purchase 100. Obviously you do not want to to transfer any funds. This can be accomplished by setting the event price to $0, or temporarily setting your payment gateway to Test Gateway.
Optional) If you set the ticket price to $0 but want to display the actual event ticket price alongside the sold out notice, after completing step 2 edit the ticket price to its actual value.
Would that work for you? Fortunately you will only have to follow that procedure for the events you are transferring over. Future events will be quite easy to add.
– Brook