I think you've got the right idea; use the 'll as though you were forming a more standard contraction, such as I'll, he'll, or we'll.

There's plenty of precedent for doing it that way, from this book published almost a century ago:

“It's a biggish hole, but Jim'll be all right in a few days, never fear.”
_{Source: Jim: The Story of a Backwoods Police Dog by Sir Charles G. D. Roberts, 1919}

to this story published just a few years ago:

“You go find Aunt Bess. Me and Bert and Jim'll do the family's share of the fightin'.”
_{Source: The Pumpkin Rollers by Elmer Kelton, 2011}

As for pronunciation, why not simply mimic what the dictionaries say for other contractions?

Collins and CDO show ðeɪl for they'll, for example.

I think you've got the right idea; use the 'll as though you were forming a more standard contraction, such as I'll, he'll, or we'll.

There's plenty of precedent for doing it that way, from this book published almost a century ago:

“It's a biggish hole, but Jim'll be all right in a few days, never fear.”
_{Source: Jim: The Story of a Backwoods Police Dog by Sir Charles G. D. Roberts, 1919}

to this story published just a few years ago:

“You go find Aunt Bess. Me and Bert and Jim'll do the family's share of the fightin'.”
_{Source: The Pumpkin Rollers by Elmer Kelton, 2011}

As for pronunciation, why not simply mimic what the dictionaries say for other contractions?

Collins and CDO show ðeɪl for they'll, for example.

For words like scorpion'll and Jim'll, try looking at words that end with a similar end sound, such as funnel (ˈfʌnəl) and camel (ˈkæməl).