delericho
Legend
Being prone is similar enough to having cover that I'd allow a character to use it for stealth, as long as opponents are not too close (withing reach of a reach weapon for your size category seems reasonable - it is the angle of observation that matters, and taller creatures have both a better visual angle and longer reach. So 2x normal reach).
The big question is if "falling prone" or a 5 ft. step is considered movement. Since Stealth is a part of movement, this is vital. I'd say it is - the rogue does need the help.
The Pathfinder SRD explicitly covers this: you cannot use Stealth while attacking. It does provide an exception to this (appropriately labelled "sniping") which allows a character to make an immediate Stealth check (at penalty) to remain hidden... but again, it specifies that this can only be done after the character takes one attack.