Keeping the Minolta 5400 flash awake

I got no response to this question on the Minolta site so I hope someone here might have the answer.

I use my old 5400HS and 5400xi  flashes for fill and, unfortunately, they go to sleep in less than 4 minutes unless they are triggered. Once asleep, the ON/OFF button must be manually pressed to turn the flash back on. Sometimes this is very inconvient. Is there a way to keep them from entering the power saving sleep mode?