A custom order can be made in a situation where you would like a free gift that is not listed as a gift on the referral website. Several of the referral websites active on eXceem offer custom orders, but some have set rules as to when you can and cannot obtain one.
To ask for a custom order, it is best to contact the website's support with the items you require, and a quote of the number of referrals required will be given to you.