I do think the big issue would be gear redundancy since a Sturmey AW has a normal 1:1 second gear with a 25% high and 25% low on each side. The 3 cog SA adapters for a rear derailleur typically had close ratios to help fill in the rather large jumps in the IGH. My instincts are telling me that's not how a front triple would roll out.

Too tired to do the math and I'll leave for the more adept geeks on the forum.

Edit I guess you could just use a claw derailleur set static in position under the rear cog without a cable?