This is what I think you should do. Find one of your female friends who is pregnant. Then get her to piss on your pregnancy test Then it will be positive. This plan could work for about a month or until your partner finds out you don't have a bump yet.please tell your partner the truth after a while or they will have you for building their hopes up.
Or just get one of these...it is always positive! (Prank Pregnancy Test) http://www.prankplace.com/product.aspx?d=New-Items.Fake-Home-Pregnancy-Test&p=28062&c=232
Please, check this previously answered question as well: