DD-5 E/D mod?

[Primus]

DD-5's have a setting called E/D that splits effect only and delay only to the two outputs. The usefulness of this is for signal routing like chaining on a second delay or adding an effect to the delay only for spaced out sounds. Anyway, the problem is that the E/D setting is fixed on a 400 ms delay range. How can I increase the delay range for that particular setting? Here's a schematic (incomplete):

http://www.cruachan-audio.pwp.blueyonder.co.uk/schems/dd5.jpg