SME Tonarms, SOTA Vacuum Turntables, and 10" Records

I have a SOTA NOVA V, an SME IV.VI, a Dynavector xx2mk2, and lots of great 10" jazz lps. As a result of the vacuum lip and the tapering tubular tonearm of the SME, playing a 10" lp is not possible because of the lip not making vacuum w/the platter. Hence, I am using a 12" crappy thin lp as a means to make vacuum and I place the 10" on top of the crappy lp. The 12" lp becomes my platter. Being the best fidelity and surfaces of the 10" lps are found on the the Bethlehems and the Blue Notes, their fidelity is not really degraded by the slight decrease in VTA that is a consequence of the increased platter height.

Am I the only one doing this? As far as a blank disc, the only ones I know of are the Johnny Winter Second Winter side 4 and a Mosaic lp set w/an odd number of sides.

I am an authorized SOTA distributor and when I mentioned it to Donna it was a bit of a surprise to her that it is happening. My other tone arms DO NOT taper so on my other SOTA's I do not have this problem. It is more of a bad synergy than a discrete problem. So for now, I am getting good use out of a very bad 12" lp!
Sorry, I'm not clear on this. I understand that the vacuum platter cannot make a seal on the 10 inch record. So, what's the problem with turning the pump off, and just playing the 10" record? At least your VTA would be correct. That would seem to me to be more important than the vacuum clamping, perhaps use a standard spindal weight? Like you would on any other 'table? Can you hear a major difference between playing a 10" laying flat on the platter, or the 10" laying on top of the 12" that's vacuum clamped? 

I remember some super cheap records I had as a child, Superman serials from old radio broadcasts. The vinyl was nearly as flimsy as a piece of paper, super thin. Perhaps that would seal and not increase your VTA appreciably? If you could find one. 

If you need a blank disc, check out Ebay for a Donna Summer 12" single side on the Casablanca label. You can get one for under ten bucks. I use this for adjusting anti-skate.
I have a vacuum clamp table (Basis Debut).  It cannot seal a 10" record.  This is not the end of the world.  Just turn off the vacuum and use the center sealing puck as a weight.  Yes, you won't get the tight coupling of the record to the platter, but, there is no point to having a blank record seal tight to the platter if there is no way to tightly seal the 10" record to the blank anyway.  
Having owned a SOTA vacuum turntable I get what the op is saying.
It won't suffice to just turn the vacuum off ... which on some (most?) SOTA models can't be done anyway as the platter motor and vacuum are controlled by the same switch.
Without a (12") lp pulling the rubber lip down flat when the vacuum is engaged, the rubber lip is angled upwards and fouls the thick part of the SME arm.
One way to get around this is to use a spacer under the cartridge
so that the whole arm sits a little higher for a given vta. This should provide enough clearance for something like the SME.
Used with a clamp the vta would remain the same for both 10" and 12" records assuming same thickness.
I have seen some spacers made of ebony and of graphite for sale. Also  the Music Man cartridge isolation device would work in this instance.

You could also use a rim weight like some other turntables use (VPI) - it would hold the lip down so it couldn't hit the platter.

Frankly, I think your solution is just fine - I own a Sota Cosmos but if I have to play 10" I just do it in y other system.