If you think you should be able to double up, first fix that 10-20 rider gappy group bit. Split up into smaller groups, get underway about 3-5 minutes apart, then you can make a judgement call. Smaller groups - 8 riders tops - get by with doubling up and taking the lane, especially if they stay close, but get more than that and it's a parade, a serious obstacle.
If it's 40-50' from the front wheel of the front rider to the back wheel of the last rider, your group is as long as an 18-wheeler, and you wouldn't want to encounter one of those on that same road, would you? Often enough on such roads, they're prohibited.