This makes no sense to me. The two roads use the same table (eg they both go through hills, and both use the hills encounter table). The GM rolls on that table, either in advance or in the moment. And the rolls would be the same either way - so what? Where is the illusion? The GM has applied the mechanic. They could even be quite transparent about it - eg rolling in front of the players, sharing the encounter table with them, etc. It's not as if the players uttering the words "We take this road" has any causal effect on the fall of the dice that the GM rolls.Rolling more frequently on the different roads means the paths have agency. It doesn't make the encounters not illusionism. If the first roll is a traveling merchant caravan, the second is a dragon, and the third is a band of mischievous pixies, what does it matter for illusionism whether the the encounters are all on the same day on the fast road, vs subsequent days on the slow road? The same rolls happen either way. It's not meaningfully different from if the GM is choosing those encounters and placing them on whichever path the players choose.