Unfortunately I think this would be like the much requested feature to have a suction ability for A_RadiusThrust. I don't remember if it was because of buggy behavior or what though. I mean, it'd be nice if it could happen, but I doubt it.
Doesn't A_Blast just use a static amount (well, not influenced by distance, anyway) of force if something suitable is in range? If negative force doesn't already work, this would probably be a lot easier than putting it in the already-a-mess A_RadiusThrust.
Graf has already no'ed this when I suggested A_Implode several years ago. The reasoning is that it won't create the results you might think you would get due to the actors being pulled towards the calling projectile will simply fly through the other side of the calling actor.