I've been using Apple Configurator to do this (you could also use iTunes to restore backups). The trick is, you need to tell the end user not to sync apps within his/her iTunes on his/her computer. You will need to instruct the end user to download apps OTA using the App Store on the iPad rather than with iTunes on his/her computer. If the user tries to sync apps on his/her computer, it will wipe out apps that you installed. However if the user downloads apps OTA, your apps and the user downloaded apps will both stay on the iPad and can be used.
Start by creating a "master" iPad backup. Use a "company admin" Apple ID when setting up the "master" iPad. Don't install apps yet. Use Apple Configurator to run a backup. Create Configuration Profiles (using Apple Configurator) with WiFi settings, backgrounds, restrictions, etc. Restore this backup onto all of the new sales department iPads.
Then if you are installing paid apps on all company iPads prior to distributing them to your users, you will want to use Apple's Volume Purchase Plan (VPP - http://www.apple.com/business/vpp/ ). With VPP, you can purchase multiple licenses using a single "company admin" Apple ID. Apple Configurator can distribute the VPP codes to each iPad and install the paid (or free) apps (you don't need VPP codes for free apps...Apple Configurator can install those easily). Then after you distribute the iPads, the user can use his/her personal Apple ID to install other apps (paid or free) via the App Store on the iPad. As long as the user doesn't try to sync apps on his/her computer all apps (company and personal) will remain on the iPad.
Here's more on Apple Configurator:
PDF: http://www.apple.com/iphone/business/docs/iOS_Apple_Configurator_Mar12.pdf
Video: http://www.apple.com/education/resources/videos/#introduction-to-apple-configura tor
Help Pages: http://help.apple.com/configurator/mac/1.0/
When you hand the iPad to the user, be sure to log out of your company Apple ID on the iPad at Settings -> Store and have them sign in with their personal Apple ID. That way it is all set for them to download apps under their own Apple ID.
Again, be sure to let the sales department know they can't sync apps on their personal computer or it'll wipe out the ones that the company installed. If they want to install previously purchased apps under their own Apple ID they can via the iPad App Store by logging in under their Apple ID and clicking on the Purchased button at the bottom of the screen.
Hope this solves your question!!
~Joe