You're welcome, Jeroen,
Yes, this can be done using SQL FTS and adding a new column to your
FT-enabled table called "ExtendedRank" and then adding an value to the RANK
value in the CONTAINSTABLE or FREETEXTTABLE query and then ordering the
results by the new column "Extended Rank". Below is an example of the query
and table structure:

CREATE TABLE FTSTable (
 KeyCol int IDENTITY (1,1) NOT NULL
   CONSTRAINT FTSTable_IDX PRIMARY KEY CLUSTERED,
 TextCol text NULL,
 ImageCol image NULL,
 ExtCol sysname NULL,
 Keyword varchar(500),
 KeywordWeight int,
 TimeStampCol timestamp NULL
) ON [PRIMARY]
go
-- Note, the column KeywordWeight may need to be re-define as FLOAT
depending upon the type of calculations you are planning on doing.

-- Insert data...
INSERT FTSTable values('This is random data for row 1', 0xFFFFFFFF, 'zip',
'random,data,row', 1, NULL)
INSERT FTSTable values('The brown fox jumped over the fence. row 2',
0xFFFFFFFF, 'xls', 'brown,fox,fence', 10, NULL)
INSERT FTSTable values('Mary had a little lamb and its fleece was white',
0xFFFFFFFF, 'ppt', 'random,data,row', 0, NULL)
INSERT FTSTable values('Moby Dick is considered on of the greatest books
available.', 0xFFFFFFFF, 'txt', 'moby,dick,book', 50, NULL)
INSERT FTSTable values('This has more to do this short text that with rows',
0xFFFFFFFF, 'htm', 'short,text,row', 100, NULL)
INSERT FTSTable values('Taglines would be helpful here as I could get more
text added', 0xFFFFFFFF, 'pdf', 'tagline,helpful,text', 22, NULL)
INSERT FTSTable values('Winston Churchill was one of the greatest speakers
of all time', 0xFFFFFFFF, 'xml', 'winston,churchill,great,speakers', 1000,
NULL)
go
-- Note, that KeyCol rows 5 and 6 have very high values in the KeyWordWeight
column

-- Test FTS with containstable and freetexttable
SELECT FTS.KeyCol, FTS.TextCol, FTS.Keyword, FTS.KeywordWeight, CT.[RANK]
  from FTSTable AS FTS
   JOIN containstable(FTSTable,*,'text') as CT ON CT.[KEY] = FTS.KeyCol
    ORDER by CT.[RANK] DESC
-- as expected two rows returned: KeyCol 6 and 5

-- caculated ExtendedRank = Rank + KeywordWeight
SELECT FTS.KeyCol, FTS.TextCol, CT.[RANK], FTS.KeywordWeight,
FTS.KeywordWeight + CT.[RANK] as ExtendedRank
from FTSTable AS FTS
   JOIN containstable(FTSTable,*,'text') as CT ON CT.[KEY] = FTS.KeyCol
    ORDER by ExtendedRank DESC  -- CT.[RANK] DESC
/* -- Returns: as expected two rows returned: KeyCol 6 and 5 with HIGHEST
ExtendedRank first!!

KeyCol      TextCol                                            RANK
KeywordWeight ExtendedRank
----------- -------------------------------------------------- ----------- -
------------ ------------
5           This has more to do this short text that with rows 48
100           148
6           Taglines would be helpful here as I could get more 48
22            70
(2 row(s) affected)
*/

Additionally, the above method is very scallable as you do not have to join
your FT-enabled table with another FT-enabled table in order to get the
"best bet" to the top of the resultset. This method could also be extended
and use a true "computed column" and support more complex calculations as
well. I don't know if this is "too much for SharePoint", but this is very
doable in SQL Server!

Regards,
John