I have no trouble with miners in my citizen milita. When not mining, they are in uniform, when mining they swap to civilian clothes. The reason it's said you need two picks per miner is if you assign your miners a pick as a weapon. I generally avoid the situation by making miners wrestlers.
This is actually a bigger problem than the "need two picks" issue. I frequently graduate to giving my civilians basic uniforms instead of clothing, but miners refusing to mine while in uniform prevents me from totally eliminating the need to ever produce replacement clothes.
Here's a snapshot of my current fort - 27 dwarfs in 6 citizen squads, 6 miners - 1 per squad. Squads rotate training through the year, so there is always one squad (incl one miner) training. Of the six miners right at this paused moment -
1 is training in military uniform.
5 are doing (Store Owned Item, Drink, Strange Mood, Eat, Construct Building) all in clothing (should be in uniform like everyone else).
3 are carrying their picks.
10 additional picks in storage.
I assign all of my mining at once each month with different priorities depending on what I want done, and just let them go and see how much they finish. At this point I'm about to designate new mining, but all mining jobs from last month are complete.
So, it would appear that I'm wrong about miners wearing uniforms when not mining. But, they are wearing uniforms to train and all of the mining is getting done, so I'm happy (or at least somewhat focused with satisfied needs).
Also, this may be a factor, I take the time to assign specific armor for each dwarf. It's possible that may be keep my miners from getting tangled up in other uniforms problems.