Here's a potential solution for Genesis Fun 14 ("Room with No Exit") that I haven't gotten around to testing on the actual Genesis game, but is worth looking into. The attached zip file contains the level in LVL format suitable for Lemmix (open with "original DOS Lemmings" style so the game mechanics match the one recorded in the replay file), and associated replay illustrating the basic idea. Actual implementation on Genesis will vary slightly due to minor differences in a bash stroke's reach, but should otherwise work. (Just make sure the fall from the 2n-thin-platform-from-top down to the 4th has some sort of stepping stone to break the fall--directly falling from one to the other would be 64 pixels which is 1 higher than the maximum safe-fall distance.) The idea of course is to reduce one round of back-and-forth walking on the left side to save time.
Cursor placement will likely need to be very exact in order to select those lemmings that need to bash the "wrong way" (instead of incoming lemmings from the crowd getting selected, which will usually be favored due to the default of later-entered lemmings getting priority). It's quite possible that in some cases the lack of pausing may even become a factor there, though hopefully not. (And remember that in some cases, if the crowd's interfering with a particular skill assignment, it may be possible to make the interfering lemming air-bash at an earlier time, to effectively shift its position away from one that will later interfere with the skill assignment in question.) And of course, it's likely that you'll get more lag frames with this solution due to needing to do more work on the left side, so I can't guarantee that even if the solution works out, its gains won't get wiped out by potential increase in lag frames.
[edit: note that the way I handled the bottom-left in the replay using a "backstroke" of the basher, it is obviously suboptimal. The position I started the backstroke at ends up moving the wall there slightly further to the left (especially with the bash mask in Genesis), a wall that the walking crowd will need to turn around at. The correct way should be to start the backstroke 1 or 2 pixels further right to avoid changing where the wall's at, or have the trapped crowd there free themselves instead of using the backstroke with a lemming outside that crowd.]