According to specification: http://www.w3.org/TR/xsl/slice6.html#fo_table
it should be possible to enter a procentage as inline-progression-dimension:

<fo:table table-layout="fixed" inline-progression-dimension="100%" >		
...

in the spec. it says under a Note:
-----------------------------------
The use of the "proportional-column-width()" function is only permitted when 
the fixed table layout is used.

If the use of proportional column widths are desired on a table of an unknown 
explicit width, the inline-progression-dimension cannot be specified to 
be "auto". Instead, the width must be specified as a percentage. For example, 
setting table-layout="fixed" and inline-progression-dimension="100%" would 
allow proportional column widths while simultaneously creating a table as wide 
as possible in the current context.

---
however when using FOP with a % it gives an ERROR:

[INFO] FOP 0.20.4rc
[INFO] building formatting object tree
[ERROR] Error in inline-progression-dimension property value '100%': 
org.apache.fop.fo.expr.PropertyException: No conversion defined
[INFO] [1]
[ERROR] At least one of minimum, optimum, or maximum IPD must be specified on 
table.
[INFO] Parsing of document complete, stopping renderer