Default value for Subject field in Case module

Default value for Subject field in Case module

I would like to add a default value to the Subject field in a custom module based on the Case module. Since this field is mandatory, I can't use a workflow rule that adds a default subject if the field is left empty.

So I would like to display a default value in the field as soon as a new case is opened. This default value can, ofcourse, be altered by the person submitting the new case, if they want, but in this case (a custom module) it would be preferred if there was a default subject.

Is this possible, and if yes, how can i achive this?

Any help is appreciated!