How can I limit DataSet.WriteXML output to typed columns?

I'm trying to store a lightly filtered copy of a database for offline reference, using ADO.NET DataSets. There are some columns I need not to take with me. So far, it looks like my options are:

Put up with the columns
Get unmaintainably clever about the way I SELECT rows for the DataSet
Hack at the XML output to delete the columns

I've deleted the columns' entries in the DataSet designer. WriteXMl still outputs them, to my dismay. If there's a way to limit WriteXml's output to typed rows, I'd love to hear it.

I tried to filter the columns out with careful SELECT statements, but ended up with a ConstraintException I couldn't solve. Replacing one table's query with SELECT * did the trick. I suspect I could solve the exception given enough time. I also suspect it could come back again as we evolve the schema. I'd prefer not to hand such a maintenance problem to my successors.

All told, I think it'll be easiest to filter the XML output. I need to compress it, store it, and (later) load, decompress, and read it back into a DataSet later. Filtering the XML is only one more step — and, better yet, will only need to happen once a week or so.

Can I change DataSet's behaviour? Should I filter the XML? Is there some fiendishly simple way I can query pretty much, but not quite, everything without running into ConstraintException? Or is my approach entirely wrong? I'd much appreciate your suggestions.

UPDATE: It turns out I copped ConstraintException for a simple reason: I'd forgotten to delete a strongly typed column from one DataTable. It wasn't allowed to be NULL. When I selected all the columns except that column, the value was NULL, and… and, yes, that's profoundly embarrassing, thank you so much for asking.

Solution

It's as easy as Table.Columns.Remove("UnwantedColumnName"). I got the lead from Mehrdad's wonderfully terse answer to another question. I was delighted when Table.Columns turned out to be malleable.