The real answer is that the annotations should be parsed to create an
ApplicationClientDD before hitting your deployer.
You're going to need something like eventually so you can create
a ManagedObject for the profile service to use.

The longer answer is that you can't do that with the AbstractSimpleVFSRealDeployer.
You'll have to write an AbstractMoreComplicatedVFSRealDeployer :-)

What you are really asking for is something that does
setInputs(ApplicationClientDD.class) (optional input) instead of setInput(ApplicationClientDD.class) a requirement.

But then you'll have to be careful about the "deployment" being null
and this code in AbstractSimpleRealDeployer

 public void deploy(DeploymentUnit unit) throws DeploymentException
 {
 T deployment = unit.getAttachment(getInput());
 if (deployment != null)
 {
 // Set the deployer type
 unit.getTypes().add(getType());
 deploy(unit, deployment);
 }
 }

Is there a reason why didn't commit your AbstractOptionalVFSRealDeployer to
the deployers project so that others don't have to "reinvent the wheel"?