Laravel 5.6 saving all fields from request and an extra field

I am saving all request fields from my model with a one liner in Laravel like this:

$imageRequest = Auth::user()->imageRequests()->save(new ImageRequest($request->all()));

My model ImageRequest has a bunch of fillables that are in the $request but there is 1 field that is not in the request that I need to save also in the table.

Can I do this in my one liner or do I need to do every fillable seperately like this:

$imageRequest = new ImageRequest;

$imageRequest->fillable1 = $request->fillable1
...
$imageRequest->fillableNotInForm = "hello";

$imageRequest->save();

via Chebli Mohamed