As Technical Manager at the National Space Centre in Leicester (Home of Extreme Ironing) I think we are qualified to comment.
We also employ one of the founders of the sport Mat Skull who unfortunately if off today or I am sure we would have personally replied.
The consensus is yes it is possible given suitable restraints to hold the target and the ironer.
If outside there would be no moisture in the garment and a steam iron would not work so expect an inferior pressed result.
Hope that helps
Say hi and good luck to John Wilton.
Regards
Graham Law
Head of Technical Services
The National Space Centre