I don't think so - the "separators" you see referenced in this forum from time to time are only useable with a 9200, IIRC. In other words, they won't work as you envision.
Again, if you don't want to have more than two cables coming into your house, but need to feed at least three receivers, I believe your only options are either DP or DPP switches, which as Nimiq has pointed out are not supported by BEV. However, lots of people on this forum use them and those people are a great help if you have problems.
You have indicated you'd like to avoid swapping LNBs if possible, which leads me to a question I've had for some time - assuming I have two "DP" single LNBs (I believe I've got at least two among the six or seven that came with the dish/receiver packages I've purchased over the years), can I use them along with "DP" SW21s (or legacy SW21s, for that matter) to feed a DP34? If so, this would avoid the need to get a DP "Twin" LNB. In your case, dharris, in a best case scenario (i.e., you have two "DP" LNBs already installed and either already have or can pick up an extra SW21 for cheap), the only thing you'd need to get to feed your three receivers off of two cables in is a DP34 switch, which you can pick up for around $20 on ebay.