from django.contrib.admin import AdminSite
from django.views.decorators.cache import never_cache

class MyAdminSite(AdminSite):
    @never_cache
    def index(self, request, extra_context=None):
        # do stuff

admin_site = MyAdminSite()

from somewhere import admin_site

class MyModelAdmin(ModelAdmin):
    ...

admin_site.register(MyModel, MyModelAdmin)