Hopefully someone can follow my explanation
Not really; I first thought that it is about a conditional value list, but since (at long last…) you state that …
I can easily get a list of IDs for Formats from "HT Values" that are "allowed" in the context via eSQL and store it in a global field.
… that doesn't seem to be the problem; so does your actual question boil down to
“How can I resolve a foreign key to display a value from the table where that key is the primary key without actually using a relationship, since I feel that adding an additional TO for that purpose would clutter my RG?”
I think what you're looking for is showing a related text value while the field holds the id.
I this case set the field to pop-up menu instead of drop-down list. The value list should be: first field ( id ), second field ( text ) and set to "display values only from the second field".
Unfortunately, you have to click the menu to unfold, unlike a drop-down but I haven't found a workaround for this.
Actually can't be bothered. It works.
a popover (new with FMP13) with a portal containing the criteria's to choose.
Have a Button with script in the portal to have ID from chosen portal inserted into Product::ID, followed by "close Popover"