With RE:Search:
1. Open the constituent record and select the Prospect tab
2. Highlight Gifts to other Organizations
3. Enter the appropriate information in the grid to the right

Without RE:Search: 
Create a separate fund for the gifts.

OR

Create an attribute on the Attributes tab of a constituent record.

OR

Use a unique gift type, such as Other, that is not used on any other gifts in the database.

OR

Create a subtype unique to the gifts.