I would do a series of soft grunts like you are a buck following a hot doe. Very soft. Remember the key is, you do NOT want the other buck to know where you are (obviously). So the softer you make it, you trick him into thinking "hey I have to walk past this deer stand to get to that sound".
The other thing to consider, if a buck is soft grunting, he very well may be hooked up with a doe already and he doesn't care about another buck in the territory. You might try not grunting at all.
Rule of thumb, after a grunt sequence, wait at least 15 minutes before you do it again.