I have had a play, you can get fairly close to this functionality, but I can't quite get there and I do need to .
If you set the UL tags style to 'display: table;', the LI to 'display: table-row;' and say spans with your data in to 'display: table-cell;'
It seems like the tree recalculates the value of the LI width, which causes a probelm. If I could stop this then the only problem if the table cells not lining up, which hopefully Telerik will be able to solve for us.
Attached is a screenshot of where I am up to.
I also added a small indent for each child into the UL with border-left: 5px; in the style.