You first need to create some kind of command that captures these notifications. For example in Linux you could put this simple shell script in a file /temp/report-tx
echo $1 $2
The script just outputs the two parameters passed to it. Then you need to configure MultiChain to execute this script and pass it the right parameters. For example put this in multichain.conf:
walletnotifynew=/temp/report-tx %e %s
By using walletnotifynew instead of walletnotify you'll only be informed of each new transaction once, and not get a second notification when it's confirmed in the blockchain.
More on how to use these commands here: