It's real easy, just follow these steps:
1. Launch get_iplayer
2. Enter the following command: (only have to do this once)
get_iplayer --prefs-add --modes=best
3. In a browser, click on here then click through to whichever act you want and copy the URL of that act:
4. Back in get_iplayer enter the following command:
so for Guy Garvey it would be:
Repeat steps 3-4 for each set you want to download.
Note: the initial programme index downloaded by get_iplayer only seems to include the transmitted broadcasts on BBC2 and 4 so the full url is better as it will tell get_iplayer the exact location to download the special iPlayer programmes for the full sets.