We present a technique for designing optimal transmit spectra for the HDSL2 service subject to a peak power constraint in the frequency domain. The peak power constraint might be imposed either due to engineering considerations or in order to optimize the transmission under a fixed transmit spectral mask (the OPTIS mask, for example). Using the channel and intereference transfer functions, SNR estimates, and the peak constraint, we set up and solve an optimization problem to maximize the capacity. Sizable gains in performance margins (or bit rates) result. While the technique is quite general - it does not depend on the exact choice of modulation scheme, for example - it is also extremely simple and of low computational complexity.