I found out last night that instead of trying to "gargle", i actually kind of acted like i was SLOWLY trying to clear my throat "almost like when trying to get up phlegm to spit" it worked.

Sounds gross, sorry... but it actually made made the gargle sound and caused my tongue to flutter also. Within a few minutes of experimenting, I was purring!!! It sounded much better than the lip flutter i had done before. I just need to practice it now to get the purr everytime.