The problem with an encap rinse is the actual amount of encap product left in the carpet when you are done. pre-sprarys are fairly concentrated when you consider you use about a quart of cleaner per 1000 sq ft (qt in sprayer filled to top with water and then sprayed on about 1000sq ft. thats our average).
When you get to the solution, we use the same, about a quart in the jug, filled with 5 gallons of water then diluted farther through the metering system. I havn't done the numbers but I figure about a quart to 5000 ft of carpet or so. then you are extracting this week solution. So how much encap polymer are you going to leave in the carpet? My best guess would be very very little.
Have you considered a post treatment with an encap product. Bridgepoint makes a post treatment with an alkali neutralizer and encap product in it. It is also a green product if your customers like that sort of thing. You will leave much more polymer in the carpet but it will be an extra step.