Yes, this can be done using Data Assist, the workflow will be different.
Use the Data Assist wizard to create pages for managing the galleries table.
The results page will have a link to the gallery details page.
On the gallery details page, you can create a link to the gallery images update page, in that link pass the gallery ID as a url variable
you will need to create the gallery images update page.
Create a recordset that uses the gallery ID URL variable to look up the images that relate to the gallery
create an upload form to upload a new image, and use the image upload behavior.
in the form include a hidden element that captures the gallery ID URL variable.
add an insert record behavior to save the uploaded record file name and gallery ID.