Just a point to note for this method:
when visitors click on your link and land on the sales page of the merchant site, your affiliate link will be exposed if they click on "View/Page Source" or right click "View Page Source"
The only way to cover up is to change readable affiliate link in source page (eg. hxxp://XXXXX.merchantid.hop.clickbank.net) to unreadable html code (which is called
numeric ampersand entities) to this (eg. &# 104; &# 116; &# 116; &# 112; &# 58; &# 47
- Remove the spaces in between
Hope that helps =)