Until the girls' bodies were found, I thought there may have been a (small) chance the bicycles were staged.
Since the girls' bodies were found, I am now convinced there was no staging.
If the girls' bodies had been found close to Evansdale (within a 5 mile radius), I would still be considering staging. But they were found well outside the search perimeter, which indicates to me that the perp's intended method was to grab and run. As long as the perp had 5-10 minutes to get out of town, he was out of danger of immediate apprehension.
It would have taken at least 10 minutes to grab the girls, transport the bikes to Meyers Lake and stage them. What reason would he have to spend that 10 minutes in town when he could be hightailing it out of town to a place he knew was unlikely to be visited by humans that day?
Then add in that search dogs apparently did indicate on the girls' scent at the scene and that some witness(es) placed the girls on Gilbert as late as 1:00 pm. It just seems to me that the evidence points towards the girls being abducted from Meyers Lake.