Problem is that there is not ECP Grenade Class name, Grenade you throw in OFP is classed as regular bis grenade, but I suspect that ECP team has used fired event handler to replace default grenade and substitute it with their model witch is probably thing class (Witch would explain rolling and animation).
In the meantime, I managed to make a simple script to do the desired effect, might me kinda complicated but here it is:
; Create ECP Grenade model and setpos it 4m above Nade1 unit (Invisible H in my case)
ECP_GRENADE= "ECP_MKIIDummy" CamCreate [(getpos Nade1 select 0), (getpos Nade1 select 1), (getpos Nade1 select 2)+4]
; Rotate the grenade 90 degrees so grenade is sideways
ECP_GRENADE setdir 90
; "Bump" the grenade to the right and up a bit
ECP_GRENADE setvelocity [10,0,1]
; It should take grenade 1.05 seconds to reach the ground (in my case)
~1.05
; Bump the grenade again to achieve bouncing effect
ECP_GRENADE setvelocity [5,0,2]
; And again
~0.38
ECP_GRENADE setvelocity [3,0,1]
; After 2 Seconds create explosive BIS grenade to simulate explosion
~2
EXPLOSIVE_GRENADE= "GrenadeHand" CamCreate [(getpos ECP_GRENADE select 0), (getpos ECP_GRENADE select 1), (getpos ECP_GRENADE select 2)-0]
; Delete the "fake" grenade
deletevehicle ECP_GRENADE
exit
Needs a little tweaking on detection when grenade has hit the ground but generally thats it.
EDIT: I'll leave the thread unsolved because someone might find out ECP's way or make simpler script than mine.