if you don't mind hacking the system up a bit you can install an external-to-the-pump fuel check valve like the ones used on my old 760. You can buy this from FCP pretty cheap.
I was intimidated by the vinyl fuel line system at first but now see it's many benefits and feel pretty comfortable with it. Find a local store that sells all the various lines and fittings and clamps and you'll be fine. Volvo seems to use 5/16" fuel line.
Judging from a quick look on FCP it looks like this 'external' check valve was last used on the 1994 940
http://www.fcpgroton.com/product-exec/product_id/5160/nm/Volvo+940+Turbo+Fuel+Pump+Check+Valve+1991-1994+(Bosch)
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1998 V70 AWD->FWD Turbo 200k+
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