Have you tried reading anything by James Connoly. He reconciles the left with nationalism quite eloquently.
Leaving aside the fundamental difference between the relationship of Ireland to Britain in 1916 and Wales to Britain in 2008, Yes, actually I have. Though I'm not sure what relevance someone talking in a colonial context has to Wales. Incidentally, we should always criticise the politics of nationalists engaged in genuine liberation struggles, for example the PLO or Sinn Fein, in that their nationalism being cross-class leads them to seek an accomodation with Empire and the Ruling Class.
Connolly argued the middle and upper class leadership of the nationalist movement had a record of betrayal in his polemics against nationalists like Grattan and O'Connell on the basis that they feared the masses more than the British because a movement from below might threaten their class position and wealth. This has affinity with Trotsky's theory of permanent revolution that only the working class can be relied upon to consistently fight against imperialism.
Connolly was the guy who on the eve of the Easter Rising cautioned his men that
In the event of victory hold on to your rifles, as those with whom we are fighting may stop before our goal is reached. We are out for economic as well as political liberty.
In
Labour in Irish History, Connolly has some beautiful passages where he highlights the role that workers struggles have made in the fight against imperialism in comparison with the politics of nationalism.
For Conolly nation never came before class:
If you remove the English army tomorrow and hoist the Green Flag over Dublin Castle, unless you set about the organisation of the socialist republic your efforts would be in vain. England would still rule you. She would rule you through her capitalists, through her landlords, through the whole army of commercial-industrial institutions she has planted in the country and watered with the tears of our mothers and the blood of our martyrs. England would rule you to your ruin.
Connolly not only polemicised against natinoalism but stressed the need for independent working class organisation even while working in a united front during 1916 to oppose British rule.
There is an ambiguity in some of Connolly's phrasing when he talks about the cause of labour being Ireland and Ireland being the cause of labour and irish for the irish, but a guy who wrote stuff like this I think is very clear where he stands:
After Ireland is free, says the patriot who won't touch Socialism, we will protect all classes, and if you won't pay your rent you will be evicted same as now. But the evicting party, under command of the sheriff, will wear green uniforms and the Harp without the Crown, and the warrant turning you out on the roadside will be stamped with the arms of the Irish Republic.
Now, isn't that worth fighting for?
And when you cannot find employment, and, giving up the struggle of life in despair, enter the Poorhouse, the band of the nearest regiment of the Irish army will escort you to the Poorhouse door to the tune of St. Patrick's Day.
Oh, it will be nice to live in those days...
Now, my friend, I also am Irish, but I'm a bit more logical. The capitalist, I say, is a parasite on industry...
The working class is the victim of this parasite - this human leech, and it is the duty and interest of the working class to use every means in its power to oust this parasite class from the position which enables it to thus prey upon the vitals of Labour.
Therefore, I say, let us organise as a class to meet our masters and destroy their mastership; organise to drive them from their hold upon public life through their political power; organise to wrench from their robber clutch the land and workshops on and in which they enslave us; organise to cleanse our social life from the stain of social cannibalism, from the preying of man upon his fellow man.