A customer ordered a plain burger on a bun cake, no condiments, no sesame seeds. I want to make the burger look really authentic. I plan on covering the "burger" part with homemade MMF. Is there something I can use on top of that to make the burger look juicy and greasy? I need it for next week. Thanks all!

Plain hamburger... not nearly as fun!  You could cover the cake in a medium brown fondant and then make sure you make it bumpy and lumpy alll over.   Mix up a glaze of dark brown gel or even black food coloring and corn syrup and paint it making sure to let it pool up in the crevices.

Plain ole burger. ..yup...oh well lol. Do you think the gel will  affect the flavor? I'm  govering the burger with chocolate fondant. 

It will probably make it a bit sweeter, but the cocoa will replace some of the powdered sugar in the chocolate fondant, it will be fine, a little stickier but fine. 

Thanks so much!!! That was very helpful.  I feel better about making "just a hurger" ;)

And I  wish auto correct would stop helping me "spell" :P

You and me both!