If you have a) a lot of extra data and b) software to accurately specify the coordinates for your data export, you can generate multiple TERs with the same center but increasing size (decreasing resolution).
My Tetons project uses a 40-50km square of 10m DEM data surrounded by 90m SRTM data. Using a series of 5 2049x2049 TERs, each double the size of the previous, I end up with a 320km terrain for 1/3 of the file size of a single 8193 TER. TG2 blends the borders of these TERs very nicely as long as the resolution jump isn't too great.