Assigning only a part of a contribution to a Contribution Page
As far as I know, since the link to the contribution page is determined by the source of the contribution as opposed to its individual line items, I do not believe this is currently possible. Even if you recorded two separate contributions, unless you have a corresponding contribution page for each (which would indeed be confusing as you state), they would both still be associated with the same contribution page

You may want to research alternative methods of pulling this information by line item financial type into an alternative widget - my knowledge of widgets is limited.

Hope this helps,
Tamar