Display form fields as view only user in admin site

I am trying to separate view only form representation and edit form representation in the django admin site.
For example I use TinyMCE for editing a changelog field (CharField) in the admin site which works great.
However when having a user logged into the admin site who has only view vermissions set, the tinymce is not shown at all but only the plain not interpreted HTML code of it. It would be great to format this html to the user to read only. How can I do that?

My Model (look at changelog field):

class UnitVersion(VersionDbModel):
A class representing version of a unit or component. Each version object (or instance of a unit) is linked to a unit defined before.
id = models.AutoField(primary_key=True)
status = models.CharField(max_length=20, verbose_name=“Status”, help_text=“Freigabestatus der Version”, choices=StatusType.choices, default=StatusType.DEVEL)
date = models.DateField(verbose_name=“Versionsdatum”, editable=True, default=now)
version = models.CharField(max_length=10, validators=[validate_version], help_text=“Eindeutige Versionsnummer”, verbose_name=“Version”, blank=False, default=“1.0”)
changelog = models.TextField(max_length=2048, help_text=‘Änderungen in dieser Version’, verbose_name=“Changelog”, blank=True)
comment = models.TextField(max_length=2048, help_text=‘Hinweise für die Fertigung’, verbose_name=“Fertigung”, blank=True)
creator = models.CharField(max_length=32, verbose_name=“Ersteller”, blank=False, default=‘unbekannt’)
created = models.DateTimeField(verbose_name=“Erstelldatum”, default=now)

AdminModel and Form:

class UnitVersionAdmin(FieldsetsInlineMixin, admin.ModelAdmin):
date_hierarchy = ‘date’

formfield_overrides = {
    models.CharField: {'widget': TextInput(attrs={'size':'20'})},
    models.URLField: {'widget': TextInput(attrs={'size':'255'})},
    #models.TextField: {'widget': Textarea(attrs={'rows':4, 'cols':40})},

# Plugin FieldsetsInlineMixin used to position Inlines in fieldset! 
fieldsets_with_inlines = [
    ('Version',             {'fields': ['unit', ('version', 'date', 'creator', 'created'), 'status']}),
    ('Kommentare',          {'fields': ['changelog', 'comment']})
form = UnitVersionForm

class UnitVersionForm(forms.ModelForm):
unit = forms.ModelChoiceField(
changelog = forms.CharField(
widget=TinyMCE(attrs={‘cols’: 80, ‘rows’: 30})
comment = forms.CharField(
widget=TinyMCE(attrs={‘cols’: 80, ‘rows’: 30})
class Meta:
model = Unit
fields = (‘all’)

Only the relevant parts should be shown here.
So the question is, how can I modify the form fields shown when using a view only user in the admin page?

There may be other options, but the easiest way I can think of is to override the get_form method in your ModelAdmin class to modify that field after the form has been created.