from django import forms
from django.contrib.admin import widgets

class ScheduleAdminForm(forms.ModelForm):

    profiles = forms.ModelMultipleChoiceField(
                widget = widgets.FilteredSelectMultiple('Profiles',False),
                queryset = Profile.active_objects.all(),
                help_text = "this doesn't show. bummer.")

    class Meta:
        model = Schedule


class ScheduleAdmin(admin.ModelAdmin):

    form = ScheduleAdminForm

admin.site.register(Schedule, ScheduleAdmin)

http://snipt.net/mandric/modify-admin-field-to-use-specific-queryset-and-form-widget/

modify django admin field to use specific queryset and form widget

form, django

Django