For the standard Form listing, the list only sorts alphabetically, so you need to develop a flexible naming convention for your forms.  Use the naming convention to control the Sorts.  Special prefix to group them.

An alternative would be to come up with a technique to have Forms selected from a pick list or a Menu Button  vs. the Menu tree.
   
In that case, you could probably control the order that list appears.  You could have a database of Forms with an element for sorting sequence.  Insert values with increments of 10 to allow future insertions just like old basic programming statements.

This is true for Forms and for Reports also.

Take a look at RelabelTreeItem function, Programming Guide, p. 351 (Version 2), p. 122 in Version 1.