Yes you can do this with Forms 9.2.
When you configure a User Task, you have the option to select a specific user from the drop down. However you also have the option to enter a variable. What this means is that you can select a Target of Delegation by typing their account into a field, and using the field value as a variable that will be placed into the User Task target.

It then makes sense to add a Delegate button to the Managers user task, and an exclusive gateway that will split the Forms path depending on if the Manager submits or delegates.
The delegation path should send the Form to a User specified by the value in a Target of Delegation field.
When I did something similar in the past, the delegation was to domain accounts and so if you want the manager to type a domain account in, you might want to consider adding in field constraints to minimize human error, or alternatively, provide a drop-down list of options available. Even better, populate that drop-down list using a lookup rule or stored procedure so that the list will update automatically when appropriate users are added to the domain!
As is the case for Forms, those users will need to be licensed and authenticated to participate within this process.