You can probably find a script in the library that will handle this for you. If you still want to do the maintenance plans you have to hack at it. You'll need two plans, one that does transaction log backups and one that doesnt. Then - Im sorry I dont have the name handy which isnt helpful - there is a table that is in MSDB that contains the db names to be processed by each plan. So you would need a job that right before the maintenance plan to add/remove the appropriate rows from each plan. Or you could just ignore that category of error, but be cautious about just ignoring errors easy to miss an important one amidst the noise.