Why?
Just adjust the thin areas and job done!
FYI - I adjusted your model to show correct sizes in NetFabb, but I work in mm so that's what I showed - it ain't rocket science to convert measurement units
Anyhow, go check out
https://www.shapeways.com/design-rules/stainless-steel-under- 3-mm , sometimes rules can be broken
but for WSF under 0.7mm walls have the possibility of having parts break off during the print thus ruining the whole print run which still has to be paid for by Shapeways, so understandably Shapeways can be quite strict about their requirements to ensure your model is economically printable.
To summarise;
Read the design rules for your chosen material.
Use NetFabb Basic to measure your models.
Adjust your model to comply with the design rules.
Job done!
Edit:Spelling re-corrected (summarise had an 's', coz I'm proper English
)