Here is Lil' Wayne performing "Got Money" and "Lollipop" on Saturday Night Live (September 13, 2008). Mack Maine appears on "Got Money."
Wayne gets on the guitar around the 8:00 mark during "Lollipop." Michael Phelps provided the introduction.
Update: The original video on Youtube became disabled. Here is another link to "Lollipop" with Wayne playing guitar although this version is much lower quality: