This is a good question, @vvcounseling, and the information and rationale in this post is still accurate.
We are aware that the broad “all spreadsheets” scope is an issue for some users. Our add-on roadmap includes a number of initiatives & changes to narrow the scopes needed to use Tiller’s tools and templates, including some research that is active presently. The truth is that these changes are non-trivial and will take time to roll out.
We are also investigating workflows that would allow for manual template insertion, but that workflow is not available at this time.
One approach you could try is to create a new spreadsheet (doesn’t need to be linked to a Tiller account) in a disposable or non-business Google account, install the needed templates into that spreadsheet, and then manually copy them into the business/restricted spreadsheet. This is essentially the manual-insertion process you are requesting with just and extra step for the in-between account.
Sorry we don’t offer a more seamless solution with restricted permissions at this time.
Randy