Per Sitecore support, this is not currently possible. However, I was able to achieve what I wanted by adding a jQuery AJAX call to the campaign URL to the sublayout used by the page type in question. Naturally this only works for clients with JS enabled, but for my purposes, that is not an issue.
<script type="text/javascript">$(function() { $.get('/?sc_camp=[campaignid]'); });</script>
Edited 2014-05-19
I found a way to do this via the Sitecore API. This is rough and needs to check for null values, exceptions, etc., but it does work:
string cookieVal = Request.Cookies["SC_ANALYTICS_GLOBAL_COOKIE"].Value;
List<Guid> guids = new List<Guid>() {
new Guid(cookieVal)
};
Guid automationStateId = new Guid("{24963AE9-1C8C-4E18-8EEE-01BC249D1F1B}");
Guid automationId = Sitecore.Context.Database.GetItem(new Sitecore.Data.ID(automationStateId)).ParentID.ToGuid();
Sitecore.Analytics.Automation.Data.AutomationManager.Provider.CreateAutomationStatesFromBulk(guids, automationId, automationStateId);