You can pick up Stylish for Chrome or Firefox and then apply the following CSS to display specific characters only on the character select in matches. For example, this one will display Falcon, Ganon, and Luigi. You can modify the IDs for any characters you're personally interested in.
.character_picks .character_for_game_melee
{
display: none !important;
}
/* character_id values
Bowser - 43
Captain Falcon - 48
Donkey Kong - 49
Dr. Mario - 58
Falco - 59
Fox - 50
Ganondorf - 60
Ice Climbers - 44
Jigglypuff - 61
Kirby - 51
Link - 52
Luigi - 62
Mario - 53
Marth - 63
Mewtwo - 64
Mr. Game & Watch - 65
Ness - 54
Peach - 45
Pichu - 66
Pikachu - 55
Random - 69
Roy - 67
Samus - 56
Sheik - 46
Yoshi - 57
Young Link - 68
Zelda - 47
*/
.character_picks .character_for_game_melee.character_id_48,
.character_picks .character_for_game_melee.character_id_60,
.character_picks .character_for_game_melee.character_id_62
{
display: inline-block !important;
}