LOTS of ways to go in order to extend the overall gear range of an IGH from using the SRAM Dual Drive to multiple front chain rings with a chain tensioner or rear derailleur adjusted to act strictly as a chain tensioner. Using thin Shimano or SRAM dished IGH rear cogs allows fitting of two cogs to most Sturmey Archer hubs. With careful choice of cog sizes and chain length the chain tension adjustment of most horizontal dropouts should be enough to allow proper chain tensioning with the chain on either sprocket. No changing of chain position possible while riding but a quick stop allows readjusting to the range wanted.

Almost all have the disadvantage of losing the simplicity of appearance and single chainline that the IGH with single sprockets front and rear provide. They also make fitting a chain guard much more difficult. The one exception is the Schlumpf dual drive front crankset or something similar. Expensive solution though. I personally favor choosing a IGH that provides the overall gear range needed to start with. If you need a wide range the Rohloff has a 526% range, the NuVinci has a 350% overall range and the SRAM iM9 has a 340% range.

As already mentioned too, trying to fit too low an input ratio for the hub via fitting a too small inner chainring risks over torquing the IGH unit which risks possible failure. Rohloff, NuVinci and SRAM all list recommended minimum input ratios for their hubs and Sturmey Archer used to prior to the Sunrace take over.