Probably the cheapest solid solution, if you are using a head with an Arca Swiss compatible clamp, is to just buy a long Arca plate and attach it to the tripod mount on the bottom of the camera with the plate extending forward under the lens. The A 70-210/4 is not that heavy a lens (in comparison to fast ultra and super tele primes and zooms), and you should be able to easily balance the kit with something like this:
Desmond DPL 169 169mm QR Lens Plate Quick w Backstop Arca Swiss Compatible New | eBay
If you feel you need more support for the lens, you can easily fashion a DIY front lens support to attach towards the front of the plate,
From experience, it's worthwhile to get started with Arca compatible clamps and plates for QR instead of getting into some head with a proprietary QR system. This might cost you more to start, but if you see tripod use as a continuing technique, some foresight will pay off in the long run. There are simply almost infinitely more mounting solutions with the Arca system than any of the others. There are already quite a few lower cost ballheads available using this system, and more are appearing every day. Most of the newer Chinese and Korean mfgs seem to have adopted the system for the most part, in addition to the higher end American and European mfgs. Even Manfrotto, probably the largest of the previously proprietary only QR head mfgs has conceded and is now making Arca Swiss compatible clamp conversions for their heads. If you already own a head that works for you, but doesn't use an Arca clamp, you can most likely find an Arca compatible clamp that can be mounted on your present head.
Take a look at Hejnar Photo's site to see how many possibilities are currently available.
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Scott