Advance wagering and the two-tiered post position draw format are the only impediments to Churchill Downs employing an also-eligible procedure for the Kentucky Derby (gr. I), according to a track spokesman.John Asher, Churchill's vice president for communications, said Churchill will review the also-eligible question, as it does for all aspects of the Derby and Kentucky Oaks (gr. I) once the races have taken place.The question of whether Churchill should use an also-eligible system, in which horses are placed on a stand-by list and can be accepted into the Derby starting field should any defections occur, came up following the scratch of Wimbledon and St Averil Friday morning.Under present rules, the Derby field is fixed once entries are taken on the Wednesday before the race. If more than 20 horses are entered, the 20 starting berths are determined by purses earned in graded stakes. Once the starting field is set, no other horses will be accepted into the field. This year, Eddington and Rock Hard Ten were entered in the Derby but did not qualify for the field because they lacked sufficient graded stakes earnings.Asher said the fact that wagering on the Derby begins Friday and the method in which trainers get to choose their horses' starting post positions are the two reasons why the Derby does not consider also-eligibles. Asher said owners and trainers spend a lot of time considering race strategy and running styles for their horses in selecting their preferred post positions."We are very disappointed those horses are not in the field; we would loved to have had them," Asher said of Eddington and Rock Hard Ten. "I know how frustrating it is for them, especially since we had two scratches. Where do you put (the new horses off the also-eligible list) them? Do you just move them into the post that opened up (with a scratch)? It is something we will look at, as we do every year. But those are the two areas that make it difficult."