Yes, I've sort-of done it.
In my case, certain tiddlers format the tiddler body as a set of css columns with fixed height(s). Those tiddlers then scroll horizontally.
So, not a "storyriver", but certainly a horizontal presentation of the content with no vertical scroll at all.
.tc-tagged-bk-layout .tc-tiddler-body {
max-height:770px;
overflow-x:auto;
width: 100%;
position: relative;
columns:3; -moz-columns:3; -webkit-columns:3;
column-gap:3em; -moz-column-gap:3em; -webkit-column-gap:3em;
column-rule: 3px dotted #ddd; -moz-column-rule: 3px dotted #ddd; -webkit-column-rule: 3px dotted #ddd;
}