I just found it interesting since most of the complaints I've seen have been about the margins being too wide on most ereaders.
If the ebooks are non-DRMmed, you could try editing the CSS, perhaps by adding this to the top of the CSS stylesheet:
Code:
html {
margin-left: 50px;
margin-right: 50px;
}
Modify the 50px if the margins are too wide or too narrow.