Do you want a few hills, lots of hills or tons of hills?
Here is one of the variations that the local group does here on Saturday mornings early am.
http://www.bikely.com/maps/bike-path/Texas-Flyers-27-mile-Sat-loop It avoids some of the bigger hills like Hilltop but you could always sidetrack there if someone wants to crawl up a really steep short hill. It starts at downing middle school and does have a fair bit of climbing. There might be a few minor changes to make it somewhat flatter but this route keeps you in the more rural area of flower mound and the surrounding area instead of in the very developed high traffic areas.
They could come out and do the later texas flyers ride which starts at 9 at downing middle school and is an out and back with a break at 11 miles in. They ride a little bit faster then a social group lately but I'd be glad to stay behind with any new folks and even have an upright to blend in that I rode last weekend.
More info on that group is at their web site and the ride page is at
http://www.texasflyers.org/index.php?option=com_content&task=blogcategory&am
p;id=45&Itemid=35 I'll be out with them on the 24th both on an early ride that usually starts at 7:30 which is a faster ride and the 9am which is a social ride but a little quicker then a true 10-12mph social ride. They do have regroups and last week we even split up a bit with riders of different levels but someone in each group knew the way well.