Figured I'd update this thing since I now have something to report for those who may be interested. I went on ahead and got some cheap 1x4 lumber and created a rough window frame out of it such that the widths are attached together similar to wall framing. Before I did this though, I had to rabbit out around the interior of the boards in order to make a continuous slot for the acrylic panel to slide into. I made the rabbit so that it would be about 3/8" in from one side of the frame, and 3 1/8" in from the other side; the deeper 3 1/8" side would seal against the window trim on my current wall so that the extra few inches would be added to the total space between the current single paned window and the new acrylic panel, giving me a total of almost 8" between the exterior glass window (little more than a storm window which sets directly on the outside of the sheathing) and the interior acrylic window. The acrylic panel that I slid into the rabbits is actually composed of two individual 1/8" panels which are separated from each other by 1/16" or so. The gap is created by 1/32" x 1/2" strips of plastic that are inlayed and glued around the edges of the panels (the glue on either side of the plastic brings the gap up to the 1/16" measurement). The completed whole panel is then slide into the rabbits and the frame attached to the wall; I attached it at the top with hinges, installed a latch at the bottom, and sealed the gap between the frame and the original wall window trim with plastic weather stripping which is attached to the frame.
So yada yada, long story short, I originally had a single 1/8" acrylic panel attached directly to the window jambs beneath the trim; I've removed that panel, doubled its thickness, and doubled the air gap by attaching it to a self-made interior awning frame work. I intended to eventually fill the 1/16" gap between the two panels with oil, however I wanted to observe the effects of the doubled mass + doubled air space between the two window assemblies without the oil first. The result is that I hear only the loudest of engines, and the sound coming through the window is almost equal to the sound coming through my wall (3/8" wood siding, 3/8" osb, 3.5" fiber filled air gap, 3/8" gypsum board).
I did eventually try to fill the thin gap with oil, but even given the light weight of the oil and the small amount that I needed to add, the acrylic was more than flexible enough to bulge out to about a 1/2" gap close to the base of the panels. I attached some 3/8" strips of wood to the front and back panels to keep them from bulging out so much, though this still wasn't good enough. I then laid the frame flat on the ground and pressed the excess oil from the opening which I had poured the oil in through so that there was only the thinnest film of oil in the middle. I sealed the thing up and reattached it to the wall, though excess oil is still settled toward the bottom, causing it to bulge out a little, and causing light to distort as it shown through it. The window is 32" x 44" and the amount of oil I used was roughly 20 floz (600 ml). I need to add more support to the panes, and the oil did start leaking out, though I knew my sealing job was crap because the glue skinned over too quickly and I couldn't get it to come out in a continuous bead like if I were using caulking; I was just hoping it would barely be good enough, which it wasn't. I'd like to get some specific glue that is actually made to wield two pieces of acrylic together, and reseal the edges, though I haven't done this yet. It's used often in the construction of acrylic fish tanks.