I used to work at a factory where we used expansion foam to pack the instruments we made. That foam is similar to the foam made by curing polyurethane glue I think.
That foam was total murder to remove! Sometimes a drop would drip out onto something we didn't want it on(like the instrument case!) and it would take hours to deal with it.
We tried many chemicals and methods until we discovered 'Oil-Flo Saftey Solvent'.

This stuff worked amazingly. I don't know if it will work for polyurethane glue, but I think that it is a staple now days at auto detailer places, so maybe if you find a place that details cars, they may put some on a rag for you.

Be aware tho, that you need to test the stuff on scrap cloro-plastic first- the oil flo attacked some plastic we tried it on, yet left most totaly un-scathed..

Here's a link google turned up..

[link=http://www.bigrocksupply.com/cgi-bin/webc.cgi/st_prod.html?p_prodid=691&p_catid=28]oil flo[/link]