GulfMP

I travel regularly with a dog and I am considering purchasing a truck with a L5P. Sometimes I need to keep the dog in the truck with the ac running for a few hours when its hot outside while I work at a job site. I know extended idle times are very bad for this engine. Would using the high/fast idle feature prevent emissions problems associated with extended idle times? If so, what would be the appropriate RPM to set it at? Thanks for any help and insight into this issue.