You can achieve this by selecting "Custom Actions" at Prefs > Mapping > EyeTV and defining two of your own with this content:

1) Fast forward 
a) Add an AppleScript actor 
b) Enter "Fast forward (sticky)" as name 
c) Use this code 
tell application "EyeTV" to fast forward 
d) Make sure it is only executed on button press (but neither on release nor on repeats)

2) Rewind 
a) Add an AppleScript actor 
b) Enter "Rewind (sticky)" as name 
c) Use this code 
tell application "EyeTV" to fast backward 
d) Make sure it is only executed on button press (but neither on release nor on repeats)

Then, select the newly created custom actions for the Left (hold) and Right (hold) entries.

Best regards, 
Felix Schwarz