Maybe use a seperate transformer for the sidings mounted near the sidings. . You can use switches for the sidings and also for a block before and after the sidings. Use 2 sets of switches for the entry/exit blocks; 1 set of switches for each transformer. That way you can run a train using your existing transformer location; bring the running train to the "entry" siding and stop it. Then go to the siding transformer; turn on the siding power you desire and "exit" block; and run out the train from the siding stopping it on the "exit" block; turn on the "entry" switch from siding transformer; run that train onto siding; then go back to main transformer to run new train.