These 2 exercises are designed for people with quite severe lateral elbow pain that have difficulty gripping/lifting even light objects.
1) Isometric Wrist Extension with 1kg dumbbell.
Start with 3x10sec holds. If pain-free, progress to 3x30sec holds or increase the weight. If you can tolerate doing this every day for 1 week, progress to exercise no.2
2) Eccentric Wrist Extension
Do 3 sets of 15 reps with 1kg. If pain-free, add an extra 1kg. Complete this exercise every second day.