Unfortunately, this instrument does not really work as intended. It is way too bureaucratic, citizens do not have the patience for that. But it is understandable that member states want a high threshold because it might in theory have real consequences. My proposal is to put the threshold not at the participatory level of citizens. Signing with just your name (or a pseudonym) and a working e-mail address should be enough. Once the proposal is discussed the summary of that discussion can be e-mailed to all participating citizens. In most cases citizens cannot get want they asked for, but the e-mail should give enough insight in how (EU) democracy works and how to proceed to get what you want (change public opinion or organise a lobby for example). If you also want to improve this instrument, a good starting point is http://www.citizens-initiative.eu/can-help-save-eci-now/
