Django : customizing FileField value while editing a model

I've got a model, with FileField. When I edit this model in a view, I want to change the "current" value of FileField which gets displayed in the view form. Let me explain.

models.py:

class DemoVar_model(models.Model):
    ...
    Welcome_sound=models.FileField(upload_to='files/%Y/%m/%d')

forms.py:

class DemoVar_addform(ModelForm):
    ...
    class Meta:
        model = DemoVar_model        

views.py:

soundform = DemoVar_addform(instance=ivrobj)
....
return render_to_response(template,{'soundform':soundform}, ....)

Now I want to edit this model in my view. When I look in browser, I see the form being displayed as

Welcome sound: Currently: welcome_files/2011/04/27/15_35_58_ojCompany.wav.mp3 
Change : <Choose File button>

I want to change this "Currently" value, which describes the whole path of the file as it exits on my server. I want to trim this string to just the filename without the path. How do I accomplish that?