Assuming you actually failed or refused his quest and didn't simply not do it, save editing is probably the least-effort solution. To avoid missing out on his pre-recruitment, non-quest stuff, I'd recommend setting the following flags:
"SATELLITE_QUEST"
to 2
"SATELLITE_GRYVAIN_DEFEAT"
to 1
"FUCKED_TEYAALS_DAUGHTER"
to 1
if you want to have fucked the enemy afterwards, and undefined
if you don't
Those'll cause the game to think you won the battle and returned the disk drive to Kase, allowing you to find him at Burt's as if you were successful. Alternatively, set them all to
undefined
if you want to reset the quest entirely.