Maybe use a custom field along side with MultiSelect
? https://meta.discourse.org/t/discourse-toolkit-to-render-forms/326439#p-1603904-custom-control-110
I see some examples in core, for example:
<form.Field
@name="appliesTo"
@title={{i18n "admin.config_areas.flags.form.applies_to"}}
@validation="required"
@validate={{this.validateAppliesTo}}
@format="large"
as |field|
>
<field.Custom>
<MultiSelect
@id={{field.id}}
@value={{field.value}}
@onChange={{field.set}}
@content={{this.appliesToValues}}
@options={{hash allowAny=false}}
class="admin-flag-form__applies-to"
/>
</field.Custom>
</form.Field>
Would it that work for you?