I wouldnt ask the tech to do it on the side unless you met him on the side. Personally, when people come to one of the shops I work at and ask me to do something on the side I usually end up being offended and subsequently give them a good lashing.
"Dont you understand that working at this shop is my livelyhood? If I did it on the side for you, I would have to do it on the side for everyone. If I did all the jobs on the side, that could put the shop out of business, me out of a job, and then where would you find the guy to fix it??!!" To which they are usually like "never thought of it like that." Keep in mind some shop owners would fire a tech for taking business found through the shop for side-work. Fortunately I dont work for "oneofthose."
The only way I would ever consider asking (or taking) work to be done on the side is if the shop states they do not service that type of equipment you have...
--Kieth