Restricting users to COPY ONLY backups
You dont need to have them use COPY_ONLY. Only An intermediate LOG BACKUPS will break the LSN. What you can do is explicitly DENY BACKUP LOG to [user|group] privilege to developers or developer group. Alternatively, just create a ROLE and deny backup log to that role. So all the users in that role will inherit the permissions.

e.g.

USE test_kin
GO
CREATE ROLE [deny_log_backups]
GO
USE [test_kin]
GO
CREATE USER [Kin] FOR LOGIN [Kin]
GO
ALTER USER [Kin] WITH DEFAULT_SCHEMA=[dbo]
GO
use test_kin
GO
DENY BACKUP LOG TO [deny_log_backups]
GO
USE test_kin
GO
EXEC sp_addrolemember N'deny_log_backups', N'kin'
GO


Now test it :

backup database [test_kin]
to disk = 'C:\crap_test\kin_test_full.bak'
with compression, stats =10, init

---- ### success for FULL BACKUP 

backup log [test_kin]
to disk = 'C:\crap_test\kin_test_log.log'

 --- $$$ ERROR MESSAGE 

Msg 262, Level 14, State 1, Line 3
BACKUP LOG permission denied in database 'test_kin'.
Msg 3013, Level 16, State 1, Line 3
BACKUP LOG is terminating abnormally.