I have a few suggestions how to make it happen (by "it" i mean not to go wash yourself right afer cumming
) or even more - lick the cum from your face, hands, feet etc.
1. Get a company
I know it my be hard to tell about your fantasy to your partner, but well, i suppose it would be worth it. You can also "hire" somebody to make you do this (i guess it would be some form of domination)- i bet that some ecort would do it for money with a smile on her face - afterall for a prostitute it is easier to wank somebody and make him play with his semen than "having sex again". In 90% of cases they would go for it.
2. Try to tape yourself.
It may not help you to do this (you can always turn off the camera after cumming) but you can get into some chat, get some "net friend" to assist you . Belive me, if you tell some person that this time you gonna do this for sure and you know you are being watched by this person (perhaps you could even make him/her command you). To save your privacy you can always put a phanyhose or some mask on your face
If you do everything well, you should forfill your fantasy about playing with your cum.