It becomes very tough if this is a standalone bill, because it couldn't directly remove someone from office.
One idea would be to mandate the GC start an immediate vote on impeachment of the Deputy if the inactivity thresholds above are reached, however it's debatable how much of an effect this would have due to the 3/4 threshold for impeachment - even if we have a seven member GC again down the road, the inactive member and one 'buddy' could simply block all such impeachments. If a GC of three or fewer ever happens, the vote would have to be unanimous - including support from the inactive Deputy.
Another method could be to mandate the GC vote on a resolution censuring the inactive Deputy and recommending the region not reelect them. However this wouldn't solve anything during the current term.
---
Given this:
If Tack can identify for us what inactivity threshold he would support, we can try again on the amendment with said new threshold.
Edit: Despite some forum statements to the contrary, the provision in the Constitution is 3/4 not 4/5, unfortunately this difference is not very significant in the calculation noted above.