Route planning in CoPilot itself is easier than most sat navs TBH, a bit fiddly due to screen size, but easier than my Garmin 660. You can drag a route to influence it's path.
Haven't seen any appropriate route planning apps yet. Easy to do on PC using the likes of ITN Converter or TYRE, both of which use the Google Maps API. I prefer ITN Converter myself as it's got a cleaner interface and you can also use Michelin mapping which has all those green edged scenic routes that almost always make great biking roads. ITN Converter saves in TRP format albeit currently v8. The current CoPilot produces v9 files, however, v8 seems to work OK, not sure what the difference is? My mate used CoPilot on his iPhone for our recent Pyrenees trip and used the v8 files I produced for him using ITN Converter without issue.
As stated above, you can use RouteConverter to spit out v9 TRP files from most GPS route file formats.