plugin as parameter value

I’m trying to get only the single most recent items from each category in a weblog to displa. To do this I’m using the following code: {exp:weblog:entries weblog="blog" entry_id="{exp:getBlogRecentItems}” dynamic=”off”}

… formatting of item here …

{/exp:weblog:entries}

where {exp:getBlogRecentItems} currently returns “4266|4445|4109”, but the weblog:entries tag shows nothing. what’s up? is this a parsing issue?