Near the bottom of the config file you'll see a userSettings section. In there, you'll find two entries for AwsAccessKey and AwsSecretKey; each of those have a <value/> entry - this is where you need to add the values. Change the <value/>
line to <value>blah</value> like this:
<setting name="AwsAccessKey" serializeAs="String">
<setting name="AwsSecretKey" serializeAs="String">
You'll need both keys for this to work.