Ok I think this should work, can someone test? I'm not sure about the exact format of the meta.txt, but the keys should be correct.
For reference, I used the easyusetool link Downunder35m posted, put all the files for these voices in the 'Insert_meta_from_map_here' folder with my deviceID.txt and ran the 'Runmeformeta' file for that folder.
Stephen Fry:
[Please Register or Login to download file] meta code:
;data104.chk_Stephen Fry (Meters)
2A 1A D6 DC 2E 91 60 4A D6 96 D5 5C 34 6F 65 2C
Wallace and Grommit:
[Please Register or Login to download file] meta code:
;data114.chk_Wallace and Grommit (Meters)
7D 01 6F 7C 01 55 F4 CB 65 E9 99 55 F3 2A F0 89