You can do this by changing ring setting on LINE port.
By default, LINE port uses Ring Profile - A, Default Ring pattern 1 ... (Physical Interface --> LINE port --> RingProfile & DefaultRing)
then, just go to Ring Settings --> Ring Profile A --> Ring Pattern 1 --> Ring Pattern. The default setting is interpreted as ON (2 second) and OFF (4 second), change it to: 60;(0+4) (no ring), or one short ring with long silence: 60;(.5+400)