I've seen just what you're talking about, and with a quad-rail free-float tube it shouldn't be a problem unless it's a short barreled M4 style rifle with a very short handguard. If this is the case, I've seen multi-rail gas blocks that could accommodate the bipod with the vertical fore end grip on the handguard itself. The great thing about the AR platform is that there are a nearly unlimited number of ways to configure them.
Which reminds me that I have a stripped Rock River lower to build on... but too many irons in the fire to start that project. I bought the stripped lower early this year to have a "grandfather" gun in case Dear Leader Maobama and his Party Kommittee henchmen (Pelosi/Reed et al) got serious about AWB version 2.0. Fortunately, they are actually pragmatic enough to not attempt such political folly twice, despite their ideological compulsion to strip us of our rights... but I digress...
Mike