TMTO works because scrypt writes the memory in-order from 0 to N-1 then reads them in a pseudorandom/unpredictable order; if you didn't save all the odd-numbered words you can recover any one of them on-demand by reading the word before it and doing the mixing operation. If, on the other hand, you wrote those words in a pseudorandom/unpredictable order as well, TMTO wouldn't be possible (or at least pointlessly time-expensive).
I think what you call a word is a 128 byte block. Whatever order you generate could be trivially stored in a map of N indices,
so you could still leave out alternate blocks and use the map to find the block from which to generate a missing one?!
Worse, N/(lookup gap), so for lookup gap 4 this map will take only 256 bytes.