Booting in application and after a button press goning into DFU

Hello,

I'm trying to modify the dfu_dual_bank_ble_s130_pca10028 bootloader so my device would start with the application and after a signal (with the button) it should start the DFU so it could be updated.

I'm using th nRF51422 (pca10028) uController with SDK 11, the S130 Softdevice and nRFutil 0.5.2.

Any Ideas how i could achiev that?