I think the requirement is perfectly clear. You say that the FAA require you to do it SOLO but thats not what my copy of FARS states!
Well read the FARs properly 61.129 (4) (i)
(4) 10 hours of solo flight in a single-engine airplane on the areas of operation listed in §61.127(b)(1) of this part, which includes at least—
(i) One cross-country flight of not less than 300 nautical miles total distance, with landings at a minimum of three points, one of which is a straight-line distance of at least 250 nautical miles from the original departure point. However, if this requirement is being met in Hawaii, the longest segment need only have a straight-line distance of at least 150 nautical miles; and
whats ambiguous about that!
<<edit: That response is going to hurt. Watch for incoming.>>