As someone who has worked in administrative positions for the better part of a decade, I will say: being seen and recognized as part of the team goes a long way.

This can be simple - sending an email to congratulate your team on achieving a goal? Send it to the folks the back office positions, too, and call them out in the email as being part of the success.

A coffee shop gift card with a note that says "thanks for your work on this project" tells us that you see us, and you see how hard we work.

The more information your administrative and clerical employees have about the company goals and objectives, the more they can be involved in meeting them. Take them as true partners rather than peripheral positions - this helps them stay engaged in the work, which helps both you and them.

I'm happy to chat further about my experience - I've worked in huge corporations and small businesses and can help you brainstorm more solutions for rewarding your team.