business men are almost always going to try to get you to do more for less.
Let them know you are treating this as a professional job, and that you must charge for your time, expertise, etc. They will understand. A sales technique that I use is to point out to them that if you come to their site to shoot these execs, each of the subjects will be away from their desk the minimum amount of time possible. This is money for them. If they have to send these folks to a studio, they are going to miss a half a day at the least.
Ask the head dude what one full day of his services would be worth. (last resort).
If they turn you down, play it very gracefully and let them know that you understand the situation, and are available in the future if they should change their mind.
Whetever you do, don't offer to discount your stated rate if they turn you down. If however, they counter your offer and it is acceptable to you, make sure you explain that the lower rate comes with some less services, like no custom touch ups, or no re shoots if needed.
Business is business. Unless, of course, if you just want to do it for free.
Then they'll know exactly what your services are worth...
