I use a Delta for long and know it like my pocket.
I think it's not possible without adding a complicated interface, 'cause the Delta's a strings machine like an organ and doesn't work with a VCO, but with a fixed oscillator which's frequency gets divided into all keys frequencies.
It might be possible to electronically alter the results of the divisions, but that would make loads of chips and wires, cause you would to alter ALL KEY's frequencies.
I wonder if the Delta's case would contain all this...
However you would have a second problem to solve: The Trig IN doesn't feed the VCA but the VCF. So you couldn't trig the synth externally without lowering any key.
Korg MS20-MS50-SQ10-X911-SuperDelta-800DV-MP4-Lambda ES50-severely modded Poly800-PE1000-M500SP-Trident MkII-KPR77-DSS1-P61//EkoSynth P15//YAMAHA CS30-CP30-DX9-01V//RSF Blackbox x2//Viscount CL1-R64//SCI Multitrack-P600//Roland GR500-SH1000