You can hard code the value in the form.yml.erb but that would suggest that everyone uses the same account. If everyone does use the same account, then you can go ahead and hard code it.
In 3.0 there’s also auto_primary_group which will submit the job with the users primary group. Again, it’s not a choice for the user, but it still comes with the premise that (a) it’s a valid account and (b) it’s what the user would like to do. In these cases - the users will be unable to choose which account they want to use for the job. That may be OK.
There’s also auto_accounts in 3.0 for Slurm clusters whcih will create a dropdown menu of all the available accounts. Lastly there’s auto_groups to create a dropdown menu of UNIX groups if you don’t use Slurm but still want that functionality.