The Petra Zone

I would speculate the following:

1. Additional musicians
2. Studio wizardary

The one that Brian Tankersley did for RD was original multitracked vocals and music combined with new music tracks for the transitions. Can't recall the name of the guy that did it, but it was all keyboards, sampled drums, etc. He was a one man band so to speak.

It's a piece of cake really. It takes time to work out the arrangement. I love doing this kind of thing for bands. It adds life to their tunes in some cases.

From the liner notes:

Additional musicians "Radio Daze"
John Andrew Schreiner - Keyboards
Paul Mills - Additional keyboards
Brian Tankersley - Drums and bass
Production details "Radio Daze"
Produced, recorded and mixed by Brian Tankersley for GBT Music
Arranged by Brian Tankersley, Darrel A. Harris and John Andrew Schreiner
Assistant engineers: Greg Parker, Terry Bates, Wayne Morgan, Amy Hughes
Recorded at Skylab Studios and Recording Arts, Nashville, TN
Mixed at Woodland Studios, Nashville, TN
Mastered by Hank Williams at Master-Mix, Nashville, TN

Additional musicians "Power Praise"
Dale Oliver - Additional guitars
John Andrew Schreiner - Additional keyboards
Brian Tankersley - Additional bass and drums
Production details "Power Praise"
Produced, recorded and mixed by Brian Tankersley for GBT Productions
Recorded at GBT Studio, Nashville, TN and Bennett House, Franklin, TN
Mixed at Javelina Recording Studios, Nashville, TN
Mastered by Hank Williams at Master-Mix, Nashville, TN

Additional musicians "The Rock Block"
Dale Oliver - Additional guitars
John Andrew Schreiner - Additional keyboards
Brian Tankersley - Additional drums and bass
Production details "The Rock Block"
Produced by Brian Tankersley for GBT Productions
Additional recording by Brian Tankersley at GBT Studios, Nashville, TN
Second engineers: Greg Parker & Sandy Jenkins
Mixed by Brian Tankersley at Woodland Studios, Nashville, TN
Mastered by Hank Williams at Master-Mix, Nashville, TN