That just won't work. The space where the inner ring would fit under that scenario is already occupied by the crank spider arms. (In fairness to the questioners, that problem is immediately apparent if you hold a crankarm and a triplizer in your hands, but it’s a lot less obvious when you’re picturing the situation in the abstract.)
If you’re not the fussy type, you can just leave off the outer ring altogether and secure the triplizer with a set of single-ring chainring bolts instead of the double-ring bolts you’d use if you were including an outer ring. After bolting the assembly in place, all you have to do is adjust high-gear limit screw on the front derailleur so it won’t shift onto the now-absent outer ring before riding happily off into the sunset.
The only drawback to that approach is that it looks just awful to run a crankset—especially a nice-looking vintage crankset—without an outer ring. The usual way around that is to install what’s various known as a bash guard, pants guard or chainring guard in the outer position. That used to be a fairly common setup back in the 1960s and 70s. Stronglight actually made a great big chainring guard that came as standard equipment on the Raleigh Super Tourer, among other bikes. Whatever you call it, it’s basically just a toothless chainring, sized to be slightly larger than the next ring inboard. (If the chainring guard is too large, it will get in the way of the front derailleur and prevent the chain from shifting onto the large ring.)
Instead, I improvised one of the right size by digging up a worn-out 47-tooth 93-pattern chainring, cutting off the teeth one by one with a sharp hacksaw, and carefully rounding off the resulting rough edge with a double-cut file, followed by a single-cut file and some fine emery cloth. The whole process only took about an hour, and to me the result looks pretty good.
Assembling the inner ring, triplizer, and chainring guard was a snap—the whole thing just bolted together.
After bolting on a circa 1981 mid-cage Suntour Vx in back and a matching front, I took the bike out on a hilly 25-mile test run. The rear derailleur shifted perfectly, as I had expected. And I was pleasantly surprised by the crisp, accurate shifting in front.
Why surprised? Conventional wisdom says that a front derailleur should work best when the curvature of cage--as viewed from the side--conforms closely to that of the outermost chainring. Like most road fronts, the Vx was apparently designed for use with a 52-tooth big ring; in the photos at the top and bottom of this page you can see that it describes a significantly larger arc than the smaller 42-tooth ring I actually used.
Even so, it shifts just fine. I can't say for sure that the same setup would work equally well with any front derailleur meant for a road double, but my guess is that most road doubles should work.
Although I haven't tried it yet, I'd expect the same compact double configuration to work nicely with a 144 triplizer in a Campagnolo crankset or Campagnolo clone. As it happens, an Oregon company called BBG Bashguards (http://www.bbgbashguard.com/Cyclocross.html) seems to make a reasonably-priced 144 BCD bash guard sized for use with a 42-tooth ring. That could do away with the need to fabricate one from an old chainring, making the 144 conversion even simpler.