I have a tourist visa single entry, 60 days. However I would not like to use it on my first entry into Thailand. I'd like to stay for 4 weeks, then take a short trip to another country and return, using the tourist visa.

Is it simply a matter of telling the immigration officer on arrival not to stamp the tourist visa?

Any complications ? thanks.

It may work or it may not - if you have a visa they can say if you do not wish to use it they will cancel it.