You don't.
**** man!
There is no reason to tell a girl you are not interested unless it is obvious her feelings for you is causing her pain or harm
In fact the more girls who like you and want to flirt with you the better things are.
There is thing called "social proof." Check it out in the Bible then come back to me.
Okay, you with me now brother?
When girls like you it sends a mesage to every other chick; "prize!"
Secondly, girls can be your best asset in getting other chicks. They have friends, you can go along to chick **** that is too embarrassing for a man to go to alone, you can practice flirting, get fashion tips and get really good at relating to women.
As for this problem, obviously of titanic proportions, where they are too busy trying to seduce you to get on with proffessional business, how about just saying it straight up, "excuse me ladies, can you please stop thinking about ****ing me until we have this report completed?"
But if you really feel that you need to let them know you are not interested I would suggest asking them to come out and help you pick up chicks. That will give em the message and if they really are that high self esteem then you might just have gotten yourself a few awesome pivots.
Cheers
JJ