I would clone the Smart Search Filter control and add the weight logic there, that's what I did. It points to a Smart Search Results web part to apply additional filters.
I would try to first establish functionality. I would set the Document Name (in the Search tab of the Page Type) as a searchable parameter.
Then add a Smart Search Results web part, add a Smart Search Filter and try to use it to search for the DocumentName = "Venue" and first see if you can get just that result.
After you get that going, you can start using "Venue" for both the general search, but also a boosted specific search through the Smart Search Filter (adding the weight "^" to it).
To help you out further, in the CMSWebParts/SmartSearch/SearchFIlter.ascx.cs, look int he Page_Load around this line:
private void AddItem(string row, string value, string displayName) {
...
ListItem item = FilterIsConditional ? new ListItem(displayName, SearchSyntaxHelper.GetFilterCondition(row, value) ?? "") : new ListItem(displayName, row);
...
}
This is where it builds ListItem with the Lucene logic. This is where you add your weight logic that i put above. I generated the ListItem's value seperately, then created the new List Item with it.
double Weight = 2;
string searchLuceneValue = SearchSyntaxHelper.GetFilterCondition("MySearchField", "TheSearchValue");
searchLuceneValue = searchLuceneValue + "^"+Weight;
ListItem item = FilterIsConditional ? new ListItem(displayName, searchLuceneValue) ?? "") : new ListItem(displayName, row);
Try that out!