Months go by without a find, then they start falling in your lap while you were not even looking - anyway, here goes ...
The Practice episode, "The Firm" (#165) has a belated guest appearance by Gina Gershon playing Glenn Hall from Snoops which was a David E. Kelley show in 1999 (10 broadcast, 3 unaired).
And according to imdb, episode #18 of Throb (48 episodes, 1985-1987) has an appearance by Stephen Furst, playing Dr. Axelrod of St. Elsewhere fame (caveat: no first name is given, but the timeframe fits, so this is good enough for me so far).
Also, if anybody is interested I´ll throw in the live appearances of the Second Shift characters on HLOTS:
Grifasi, Joe (Lt. Walter Neal) : Homicide: Life on the Street: „Closet Cases” (#86/ 2-Jan-1998)
Guyer, Murphy (Det. L.Z. Austin) : Homicide: Life on the Street: „Homicide.com” (#113/ 5-Feb-1999)
Ornstein, Michael (Det. Tony Bonaventura) : Homicide: Life on the Street: „Abduction” (#94/ 27-Mar-1998), „Homicide.com” (#113/ 5-Feb-1999)
Thomas, Raymond Anthony (Det. Layton ‘Lee’ Johnson) : Homicide: Life on the Street: „Abduction” (#94/ 27-Mar-1998)
Now if someone could provide me with a Second Shift webisode and guest cast list ...