Envelope with decay, sustain or release higher than attack

[softdevca]

I am attempting to create a version of a Yamaha DX7 style preset in Phase Plant.

The DX7 envelopes have four stages where the level at each stage can be any value from 0-99. However, Phase Plant has an ADHSR-style envelope where the attack must always be the highest value. As flexible as Phase Plant is I can't seem to figure out a way to be able to convert arbitrary DX7 envelopes.

I can't use LFOs because they always move forward at the same rate. I'm not above doing something hacky.

Any ideas?