I don't think there is a standard colloquial term. Shyster frequently refers to a lawyer who is licensed but unscrupulous, who is some way steals from his clients and/or others.

Fake lawyer is used. Although not the most colorful expression, it clearly conveys the meaning - the person claims to be licensed but is not.

Here are some examples:

Nevada City Woman Under Investigation For Practicing Law Without A License
NEVADA CITY (CBS13) – A woman claimed she was a lawyer with a rolodex of clients, but investigators call her a liar, saying she never even went to law school.

The would-be attorney is now the target of the district attorney.

Sarah O’Neal’s office was within view of the courthouse, where the district attorney works. She came into town introducing herself as a big-time lawyer, but prosecutors say she’s a big-time fraud.

“She says, ‘oh I worked in federal court for so many years. I was just burned out,’ ” paralegal Rosie Freeman said of the fake lawyer.

O’Neal opened a law office in Nevada City, telling co-workers she wanted a simpler life and to help people.
It’s a nice story that prosecutors say is a lie.
“How can you just pretend to be somebody you aren’t and make their life worse? That’s awful,” said Freeman.
http://sacramento.cbslocal.com/2012/11/15/nevada-city-woman-...

Fake Lawyer Tahir Malik Tried Over 60 Cases, With No Law Degree
Tahir Malik, a 47-year-old man from Skokie, Illinois, "walked around the courtroom like he was a hotshot, strutting around," said one of his clients.

He tried more than 60 cases, charging between $500 and $4,500 to his clients. He worked on traffic court cases, mortgage foreclosures, and some low-level criminal cases.

One problem: Malik never spent a day in law school. Instead, it appears that he learned his lawyering skills from his own criminal background.

"From his own arrest history, he was familiar enough with the court system to make certain motions and file certain documents in the court," said Cook County Sheriff Tom Dart, according to the Chicago Sun-Times. "There is no question that dozens of people from all over Cook County were misled by this guy."
http://www.huffingtonpost.com/2011/01/09/fake-lawyer-tahir-m...