Oddly enough the main objection to doing that was cost - that's why recruiting was closed in 1862, the problem was money, and it's why there's a dearth of small arms in early 1862 (when every man they can arm is going to the front) but a surplus in mid 1862 (when there's 300,000 small arms stockpiled including about 100,000 "good rifled arms"). It's also probably why there was a troops crisis in mid-1862, with nobody really willing to send McClellan anything at all as reinforcements.
How would McClellan have done otherwise? He was still a serving military officer at the time, remember, resigning on election day, and wasn't a party higher-up (he was functionally a popular outsider with the D party designation) so couldn't really exert much influence on them.
With the new Congress not taking office until March I'm not sure there would have been a huge funds problem - if they turn off the money tap right then there's still a massive advantage around Richmond and the CSA is collapsing. But that assumes that there's a massive Peace Wave putting McClellan into office, where it's more likely that what would put McClellan into office is simply his relative popularity compared to Lincoln. (Even a 5% swing to McClellan, which repeated nationally would put him into office, would put the popular vote totals even for President, and if repeated for the Democrats would (e.g.) flip four seats out of nineteen in Ohio and 0 out of 3 in California - for which we have data - and would thus increase the Democratic bench from this sample from 2/22 to 6/22).
Of course, none of that really affects the salient point, which is that McClellan did repudiate the peace plank and there's nothing about his professional life that suggests he would do otherwise as a President. He did after all fight the Confederacy, and prioritized reunifying the country over other things.