You can use the mouse in combination with Keyboard shortcuts in Resolume 3.
In the default settings your mouse is mapped to the 'P' key. Hold down the 'P' key and move your mouse to position the selected clip.
1. Select Mapping->Edit contextual key map
2. Select scale parameter of clip for instance.
3. Press a key on your keyboard, let's say 'S'
4. Choose 'mouse' from the dropdown list in the mapping panel
5. select which axis you want to use, x or y
The next time you hold the 'S' key you can move your mouse to change the value.