“I’ve gotta wrinkle that’ll turn your Friday face to a giggle-mug”

What was that now?

WRINKLE:  an idea, or fancy:  an additional piece of knowledge which is supposed to be made by a wrinkle a posteriori   (Cab Calloway’s Hepster’s Dictionary)

FRIDAY-FACE. A dismal countenance. Before, and even long after the Reformation, Friday was a day of abstinence, or jour maigre. Immediately after the restoration of king Charles II. a proclamation was issued, prohibiting all publicans from dressing any suppers on a Friday. (1811 Dictionary of the Vulgar Tongue by Francis Grose)

GIGGLEMUG:  “An habitually smiling face.” (1909 Passing English of the Victorian era : a dictionary of heterodox English, slang and phrase by James Redding Ware)

So, basically, “I’ve got an idea that’ll turn your frown upside down.”