The easiest approach is to use one of the larger chips, but I understand the temptation to stick with -1701. I need so much I/O in my design that I just went with two -1701s.
For a single -1701 solution, I have only done downsampling, but the principle is the same: you use an upsampling filter, then perform your process at the single speed rate using two or four streams that feed each other sequentially within one sample period. This is tricky if your process needs filters though, I would guess you've have to code them manually which would cost you more instructions than you might save.