I just went through this with vB3, I'm not to familiar with vB4 but I'm pretty sure it would require a plugin.
a workaround for this though could be to wrap {vb:raw lastpostinfo.lastposter} in a div and position it where ever you like which would make it appear out of the lastpostby template
an example (not recommending this exact code, just an idea)
Code:
<style>
.lst_pstr {
position: relative;
margin-top: 130px;
margin-right: 54px;
}
</style>
<div class="lst_pstr">{vb:raw lastpostinfo.lastposter}</div>