Residential client lives 2 miles from the nearest DSLAM and wants to contract me to increase his down rate by 5mbps...

A residential client reached out to me desperate for options to improve his internet situation. He lives in unincorporated King County Washington, in the rural area of Duvall. I did a bit of due-diligence and the only ISP servicing the area is the one he's already using (Frontier Communications) with the copper being leased by Verizon. They (Frontier) have him on an ADSL line. I was able to get a hold of the copper team and talk to the tech in the area. The client is currently provisioned for 3mbps at the DSLAM, but his account is provisioned for up to 20. The tech said he originally had the client at 6, but the noise in the signal caused him to drop frequently so they limited him to 3 at the DSLAM. The client is willing to pay $3-4k if I can get him up to 8 or 10 and $8-10k if I can get him up to 15-20. There's no utility poles in the area, all service is provided underground across multiple plats and easements under a shared private road. I discussed the problem with the tech and he seemed pretty confident that the client is SOL, but to let him know if I came up with anything.

Does anyone have any clever ideas on how I could potentially squeeze another 5mbps on his line? I've used extenders for VDSL in the past with some luck. Anyone have any success with extenders for ADSL? Any other ideas?