Just found out that when running batch 360 e-Synergy with Macola ES, the webshopping cart will suggest related items based on parent/child relationships you've created. The trick is to make sure the Relation Type is set to Shop Suggestion under Logistics: Maintenance, Item - Relation types.
The administrator has disabled public write access.
This functionality has been in Exact e-Synergy for a long time; it's just that the Macola ES-specific check out screen did not allow you to enter the quantities that you wanted to purchase. As "Oldman" mentioned, this has been fixed in Batch 360.
Details on how to set up this functionality can be found in document 00.797.188 (you can tell by the doc number this functionality has been around for quite a while.
You can also use the "shop suggestion" to allow you to add multiple items to a contract at one time. This is really slick if you are using contracts in e-Synergy. Details are found in doc# 8.118.553.
Realize that this shop suggestion functionality for WebShop is maintained only in Exact e-Synergy.