dont do a walkover it is a very selfish and silly thing to do
in a walkover you get no training minutes and your opponents minutes are also messed up
surely in a 13 man roster you can find two guys who need training and allocate them for all 48 minutes then find one more guy who wont get enough minutes this week anyway and dress him too
other options to consider are buying 1-3 x 1K players then firing them after the game or if you dont have guys you need to train hire a couple of 18 year olds with respectable in whatever you are training this week play them 48+ minutes then with luck they will pop to strong and you can sell them at a profit