As brogan said, a template modification would work well.
In development mode create a new option:
Option Id: aUniqueIdForYourOption
Add-on: select your add-on from the drop down
Title: Display on forum home only
Explanation: Unchecked, will display the data on all pages
Edit Format: On/Off Check Box
Data Type: Boolean
Default Value: 1
Also select Include this option in back-ups.
For the template modification:
Create a new template modification, and select PAGE_CONTAINER for the template
Find a spot you want your data placed, for example:
Find: <xen:include template="ad_below_top_breadcrumb" />
Replace with:
$0 (this is the find text to be placed back in)
<xen:if is="{$xenOptions.aUniqueIdForYourOption} && {$contentTemplate} == 'forum_view'">
your custom data on forum home only
<xen:else />
your custom data to show on all pages
</xen:if>